Guitar amp conversion
60ies Philips VE1306-02
We came across this cute little 12W Philips amplifier on eBay.
Low price, good condition, best prerequisites for a small guitar amp. we had to have it!
History
Where do you come from?
There's not much to be found on the know-it-all internet about this cute little 12W tube amp from Philips that goes by the "sexy" name VE1306-02. Ok, the engineers at that time must have found the name very sexy!
Incidentally, the engineers who came up with the "sexy" name were at Philips in Hamburg and that must have been in the early 1960s. We can't find out for sure, but online sources and the component mix in the amp strongly suggest the early 1960's.
The helpful (but complicated) site Radiomuseum.org could at least help us with a circuit diagram. 12W from 2xEL84, Cathodyne Phase Inverter ("Hello Fender Princeton"), EZ80 rectifier, and the preamp combo of EF40 and ECC40 that was very common in the 60's. Rightly so: great combo!
What was this amp originally intended for?
12W... just a mic input... just a volume knob and a mysterious "T knob". Loudspeaker output only via cable which is connected to luster terminals inside... no connections on the back... no handle for transport...
Ok, the amp was definitely not designed for mobile use, but to be permanently installed somewhere, wired up and then not moved. I suspect applications such as school auditoriums ("the headmaster is speaking!"), small community halls, churches, etc. Just about everything where in the 60s someone wanted to be heard with a microphone and then no DJ was planned for entertainment... ;-)
But anyway, the puristic design seems perfect to make a small guitar amp out of it.
The ingredients promise: AC15 meets Princeton meets Echolette. Not bad!
Meanwhile...
let's simulate
To shorten the waiting time a little, we simulate the amp using the circuit diagram from Radiomuseum.org already in P-Spice to get a feeling for the circuit.
As already suspected: Everything points to the use as a voice amplifier. Very linear frequency response, high negative feedback to avoid distortion. And the mysterious "T control" turns out to be neither a "Tone" nor a "Treble" control, but a clever "bass control" (T = Tiefen) that can effectively suppress unwanted rumble during important speeches by the headmaster.
First impression
Lucky Strike. Top eBay seller caught!
The first impression confirms the auction pictures: Very good condition... mostly original tube set from Valvo... relatively "untouched"... great! The construction of the housing at that time is always impressive. The style is very "industrial", but with the VE1306 you only have to loosen 2 screws to be able to disassemble the complete amp and have full access. Perfect!
A first screening of the circuit says that it is mostly original, but someone has already tried to "service" the amp and a few capacitors have been swapped out. The previous owner also gave the "Service Protocol" for this, which was a handwritten note. The circuit was not changed here (thats good) and good components were used... however, the "service" is somewhat questionable, since some new components were simply soldered to existing wires (sometimes rather "glued"). Individual connections have already come loose at the first touch...
Well intentioned... they didn't do anything completely wrong either... but just sloppy work. They'll have to "practice" that again.
Incidentally, according to the "service protocol", the tubes were also measured. The ECC40 was exchanged for an old Philips at the time, but the 2 EL84 are said to be in good shape and matched perfectly. Let's see...
First test
are the tubes still good?
With such a beautiful old tube set, one naturally always hopes that they are still in order or at least "usable".
In our experience, the chances of this are quite good, since the old Valvo's are among the best that were produced at the time and usually stand up to the ravages of time quite well.
So we have our eTracer fired up and put the tube set to the test:
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EF40: in great shape!
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ECC40: Just about usable, with 1 triode system weakening somewhat and drawing increased current in the limit area.
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EZ80: Well, borderline... the two diodes are clearly different, but the bottom line is they are still usable.
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EL84: One good... the other good at first glance... but unfortunately a case for the museum at second glance. Pity!
So the bottom line is a mixed result, but old tube sets are always a bit like playing the lottery. You don't always have 6 right.
Especially with the EL84 it paid off to have a real curve tracer and not just a traditional tube tester like the German Funke, the American Hickok or the Russian L3. Here, only the anode current is determined at a specific operating point and it is derived from this whether the tube is still good.
The two EL84s in our eTracer both passed this test with "Good" and a similar result. The former service technician also measured and noted this in his report. But if you actually measure the characteristic curves of the two EL84, you can see very clearly that one of the two EL84 tends to "buckle" and weaken at high currents. We would not have recognized this with a traditional tube tester.
So now it's time to search the TWS pool for a Valvo EL84 with the right values, or the amplifier gets a new set of power tubes. Let's see.
Analysis of the output transformer
our problem child.
Unfortunately, the amp already showed in advance that it does not have the 4/8/16 ohm speaker connections that are common today, but instead provides 2 connections that are named "100V" and "3V" in the circuit diagram.
"100V" is clear. This connection is intended for the 100V ELA systems that were common at the time and we can't really do anything with it.
In order to find out what we can do with the "3V" connection, we have no choice but to determine the winding ratio of the output transformer and then calculate which loudspeaker impedance makes sense here for the 2xEL84 push-pull power amplifier.
That sounds complicated at first, but it really isn't.
An output transformer does nothing more than convert a high impedance (high voltage, low current) to a low impedance (low voltage, high current). This conversion factor is determined by the winding ratio, which unfortunately is usually not specified.
So if we now know which primary impedance we want for a specific power amp configuration and know the turns ratio, then we can calculate for which loudspeaker impedance the transformer is suitable. Conversely, we can also calculate backwards for which primary impedance the transformer is suitable if we know the loudspeaker impedance and the winding ratio.
In our case we know that the 2xEL84 push-pull power amp would like to see a primary impedance of 8000 ohms and we would like to connect a guitar cabinet with 4, 8 or 16 ohms. So we need to find out if the turns ratio of the output transformer allows this.
The easiest way to measure this is to connect a potent and controllable AC power source to the secondary winding of the output transformer (e.g. a control transformer, in English "Variac") and measure the AC voltage that is fed in using a multimeter. Then (or at the same time) you measure the transformed voltage with a multimeter on the primary winding of the output transformer. If you now divide the measured primary voltage by the fed-in secondary voltage, you get the turns ratio of the transformer. By simple squaring, you can then calculate the speaker impedance for which this transformer with the present power amplifier is suitable.
!!! ATTENTION !!!:
When an AC voltage is fed into the secondary winding of an output transformer, a high current flows!
So please always start at 0 and then increase it very, very carefully. We don't want to grill an output transformer! Normally you will rarely feed in more than 10V to get voltages in the range of several hundred volts at the primary winding.
By the way, you can also find a nice video on YouTube of the iconic tube amp legend Uncle Doug in which he explains how this can be done without a control transformer.
Result:
Ok, after all that incomprehensible tech talk... what does this Philips VE1306-02 come up with?
Unfortunately crap comes out!
The winding marked "3V" would ideally require a speaker impedance of 1.2 ohms.
The winding marked "100V" would ideally require a speaker impedance of 1000 ohms.
What the hell were the Philips engineers doing back then?
Well, they have developed a "messaging amplifier" that was precisely optimised for the conditions at the time.
This was either connected to a 100V ELA loudspeaker system or 2 loudspeakers, which were common at the time, such as the Echolette LE2, each with an impedance of approx. 3 ohms, were connected in parallel. This results in a loudspeaker impedance of approx. 1.5 ohms, which fits quite well.
Neither one nor the other fits for the planned application as a guitar amp. Big crap!
The output transformer is therefore useless for this application.
We are left with 2 options:
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Leave the amp in its original state and use it as a mono amplifier for 2x4Ohm studio monitors
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Replacing the output transformer
I need to sleep on that one night. stay tuned
Little Philips...
what will become of you? The decision...
Ok, after even sleeping "several nights" on the future of little Philips, the decision is clear:
The 1306 becomes a guitar amp!
A workshop amp for listening to music would be cool... but mono isn't fun. With AC/DC I would always have to choose between Angus Young and Malcolm Young... "No-Go"!
Finding a second amplifier for a stereo setup in the workshop is unrealistic...
You could always use a 10W bedroom guitar amp though, especially with the ingredients at hand!
In addition, the following prompted me to carry out the intervention with a new output transformer:
As it is, the amp is fairly original, but just not practical.
The amplifier is designed as an installation amp and has only minimal connection options (1x microphone input).
No speaker-out, no power jack... nothing. All cables come out directly from the amp.
I always shy away from changing old amps mechanically, but here a few small interventions are simply necessary to bring the 1306 into a condition that people enjoy using it and don't just sit on the shelf.
Therefore the amp gets:
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A new output transformer for guitar use
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Speaker Out jack on the back
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Impedance selector switch on the back
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The microphone socket on the side is converted into a guitar input with a jack socket
To do this we have to drill 4 new holes in the case (destroying the original condition), but it's worth it!
Until we have found a suitable, new output transformer, we will start overhauling the power supply unit as well as the pre- and power amplifier...
Overhaul of the power supply
deep dive into the internet.
When measuring the tubes, we had already determined that the 2x EZ80 rectifier tubes are still usable.
The two old Philips electrolytic capacitors, each with 2x25uF, also made a usable impression, but as already described several times, this is a really safety-critical point where it is better not to play the lottery.
So it was clear that the two electrolytic capacitors had to be replaced in order to achieve an operationally safe condition.
Unfortunately, the electrolytic capacitors are a "problem" in old, European amplifiers.
These are usually designed as radial screw caps where the housing represents the ground contact and only the solder connections of the positive poles are brought out as pins. This is not common these days!
Current, radial electrolytic capacitors are usually attached using a "clamp" and have all connections brought out as pins.
Conclusion: Mechanically incompatible! Holes need to be expanded and new holes drilled.
Since we want to change as little mechanically as possible, the challenge is to find "new" capacitors with an "old" mechanical structure. To put it mildly, this application is "super special"!
After a lot of internet research and email exchanges with the renowned German capacitor manufacturer F&T, you will then find specialized shops like "Ask Jan First" where you have a great selection. You have to get used to the "early days of the Internet" but even today ordering by email or telephone without an online shopping cart still works quite well. According to the shop, you could also write a letter or send a fax. But we didn't do it... we did it "totally space age" by email.
"Jan" delivered quickly, and in addition to 2 new 2x32uF screw-in capacitors manufactured by F&T (slight upgrade), we also ordered some 15nF Electrica Minifol as coupling capacitors, which are not original but at least "Period Correct" .
Installing the new e-caps was pretty "straight forward"...
This time there were no other problem areas in the power supply, such as aged resistors, because the complete resistor set of the 1306 consists of extremely high-quality Rosenthal resistors, which still work perfectly and are spot on even after such a long time. Rosenthal is among the best you can find in old amps!
We are in good shape!
So for the first time in a long time, the amp was started up again using the isolating transformer and the power supply works absolutely stable and delivers all voltages as it should be.
Overhaul of the power amplifier
happy days!
Keeping a long story short:
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All Rosenthal resistors still in top condition...
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Cathode-Bias Elko still in top condition...
One of the phase inverter coupling capacitors had already been exchanged for a WIMA MKP. Actually a very high-quality choice, even if it doesn't look like it fits into the amp at all. Unfortunately, the connecting wires were simply cut off from the old capacitor and the new capacitor was glued to it more than soldered. The second coupling capacitor was probably an original Erofoil. Since, in my experience, these tend to get "leaky" over time, I made short work of it and swapped both capacitors for 2x15nF NOS Electrica Minifoil.
A quick measurement while the amp was running also showed that the NOS Minifoils are in top condition and do not let any DC voltage through.
We postpone the selection of the power tubes and the setting of the operating point until the amp is complete and has the new output transformer. Until then, the two old Valvo EL84s that came with the amp are just stuck in there.
Preamp overhaul
work to do.
Again, short and sweet:
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All Rosenthal resistors still in top condition...
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Cathode bias electrolytic capacitor on the first triode of the ECC40 still in top condition...
The second triode system of the ECC40 is used as a cathode phase inverter as we know it from a Fender Princeton, but in a somewhat simpler version without a coupling capacitor and feedback from the cathode to the control grid. Interesting! We'll leave it as it is and see how it performs...
From a purely technical point of view it can be improved, but that doesn't automatically mean that it sounds better.
We clean up...
The coupling capacitor to the EF40 input stage has also been exchanged for a WIMA MKP. Likewise the 1nF capacitor of the bass cut control network. In both cases, using the "technique" described above (which is actually just laziness) to cut off the connection wires of the old components and then somehow solder the new components to them. We corrected both and exchanged the coupling capacitor (as in the power amp) for a NOS Minifoil 15nF and the 1nF audio capacitor for a NOS 1000pF Cornell Dubilier Mica-Domino.
Yes I know, a US Domino Cap in a 1960's European amp is actually "incorrect". But it just fits perfectly into the overall picture and these capacitors sound great!
And oh yes... of course we didn't just solder the new components to old wires (standing in the air), but completely removed the previous botch and connected them neatly to the appropriate connection terminals. "Quick & Dirty" can be very attractive in other contexts, but certainly not when it comes to restoring old amps. Here in the Tube WorkShop we like it rather clean and solid.
Modification of the EF40 input stage...
Well, this one is a little "special".
A coupling capacitor to the microphone input... an extremely high-impedance grid leak resistor with 10 meg... cathode directly to ground. This is a rather "antiquated" concept called grid-leak bias and was often used in the early days of tube technology. This uses the effect that some of the electrons emitted at the cathode stray to the control grid of the tube and build up a negative potential there which can be used as a negative grid bias.
Normally, the charge flows out again directly via the grid-leak resistor. In order to prevent this, this is now extremely large (5-10 meg) and the control grid must be decoupled from the DC-moderate input signal using a coupling capacitor.
Yes... works... somewhat...
In order to make the biasing more stable, cathode biasing was quickly adopted for preamp tubes. With this you can also do without the coupling capacitor at the grid input and you are freer in the choice of the grid leak resistor (and thus the input impedance of the circuit).
Honestly, I'm surprised to find grid-leak biasing in a 1960's amp. That was actually no longer "state of the art" at the time. But who knows... perhaps an ingenious move by the Philips engineers for the microphone input? But maybe they just screwed up a bit the next morning after a night of drinking on the Reeperbahn...
In my opinion, the EF40 works much better if you give it a cathode resistor (1.5k in this circuit) and a cathode bypass capacitor of 25uF. Stable cathode bias... no stray electrons on the control grid that we have to cherish there. That's the way to go!
No sooner said than done... unfortunately we had to use a standard 25uF/63V electrolytic capacitor in the Philips 1306 due to the space available instead of the usual 25uF cathode bypass capacitors from the Tube Amp Doctor with smooth foil. But that won't be the end of the world.
Likewise, the 100nF WIMA screen grid resistor of the EF40 was exchanged for a NOS Electrica minifoil type.
Even if the old WIMA's are among the most beautiful capacitors I know (look like candies), the 100nF capacitor for stabilizing the screen grid was simply "leaky" in our amp and had to be replaced
Input for guitar
sheet metal work.
As described above, we actually prepared everything in the preamp so that the amp works well with the guitar. Unfortunately, the original 3-pin DIN input that was common at the time is located on the amp.
From a purely mechanical point of view, there is also no 1:1 replacement to convert the holes in the old DIN inputs to a jack socket.
So we're using a method here (which we've used many times before) in which the original housing opening is covered from the inside with a black aluminum sheet which has a corresponding hole for a jack socket.
With the 1306, 2 additional holes had to be drilled on the corresponding retaining plate (who counts: Those were 2 of 4 holes that change the original condition of the amp). As a result, we have converted the amp to a jack input with a visually and technically very appealing result.
First sound test
has potential!
Although the output transformer has not yet been replaced, we dare to do a first sound test. The original tube set was used, and we know that at least one of the EL84's is no longer fit.
A 16 ohm guitar box was connected, which is far from the conditions of the original output transformer.
So, is this test meaningful: "No, it's not"
But it gives us a good feeling of where we stand with the amp and what's possible.
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The background noise and the basic hum are more than acceptable
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The amp sounds very promising right away. A "treble bypass" on the volume pot is definitely still necessary
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The "low control" (which was originally designed for microphones) also does an excellent job on the guitar.
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When fully cranked, the amp also seems to be able to deliver VOX or Marshall-style distorted sounds at a high level
This is only a first test under less than optimal conditions.
But there are signs that our little Philips 1306 can become a great guitar amp...
New output transformer
the dream of my sleepless nights!
In order to give the amp a future in which it doesn't gather dust on the shelf for lack of useful use (but is used and loved), we had already decided to install a new output transformer and a speaker-out and impedance selector switch.
It doesn't sound that complicated at all. Output transformers in the 10-20W range that fit 2xEL84 and have secondary windings for 4, 8 and 16 ohms are nothing unusual now.
But if you then remove and measure the old output transformer, you will of course find that it has a size that is absolutely unusual today. And of course it is so narrow in the amp that you can't just install any replacement and drill new mounting holes if you wish. Something is always...
So what do you do in the evening instead of sitting in the beer garden?
That's right, you travel the internet all night long for a suitable output transformer. You have to be a little "Amp-Crazy" for this, but hey... in the last two weeks the weather was shit and not suitable for a beer garden.
In the meantime, I know pretty much every output transformer with a primary impedance of around 8k and secondary windings for 4, 8 and 16 ohms personally and can also name the dimensions by heart! Certainly not everyone can claim that and there are probably good reasons for it... ;-)
The decision is ultimately on a Tube Town Transformer, which is specially made for amps like 18W Marshalls in Europe. On the one hand, this has exactly the technical specifications we are looking for, on the other hand it is very close to the original transformer in terms of dimensions and has many laminations. "A lot of metal" is always good in an output transformer because it remains stable for longer, especially in the bass range.
I won't say it was a "drop-in replacement" without any problems, but with a little filing, cursing, and light tapping with a hammer here and there, we were able to move the new output tranny into the 1306 using the existing mounting hardware and screw holes to feel at home. So operation successful!
Since we were in "mechanics mode" anyway, we also installed the impedance selector switch and the jack speaker output on the back of the amp. These were the 2 remaining holes that we described above that change the original condition. So be it!
Next we can put the file, hammer and cordless screwdriver aside again and start the soldering iron to connect the new output transformer. There isn't much exciting to say about this. In the beginning you have a spaghetti tangle of colorful cables. In the end, they are laid and soldered reasonably neatly where they belong and give the amp a little colorful "rainbow flair". Incidentally, I am particularly proud of the pink cable to the speaker socket. Why? Why not?!?!
It might also be worth mentioning that we also installed a new mains cable at the same time, which is earthed via a good chassis ground and has a useful cable clamp for strain relief. Before it was more of a "fly-wire"... not good at 230V.
Equipping and measuring the power-amp
on the finishing line.
Ok, from colorful cables back to the serious side of life. The power amp needs a well-functioning tube set.
A quick test after installing the new output transformer with the old tube set showed that everything works as it should and that we also connected the primary windings of the output transformer the right way around. Can you connect them the wrong way around? Yes you can... at least with an amp that works with negative feedback from the speaker output to the preamp (like the 1306). If you swap the primary connections of the output transformer here, you turn the negative feedback into "positive feedback" which gives you an unbelievable (but very unpleasant) amplification of the output signal. So if you ever replace an output transformer somewhere and then hear "Noises from Hell"... swap the connections of the primary windings.
But actually we wanted to talk about the assembly of the power amplifier.
As already written above, the EL84 set with the amp was no longer in good shape. One of the old Valvo's EL84 still showed very usable values, the other one somehow still worked but was very weak and a case for the museum.
While rummaging through the Tube WorkShop pool of old tubes and matched pairs, we came across a single old Valvo EL84 which, according to the measurement protocol, has almost identical values to the still well-functioning tube of the tube set.
A quick check in our eTracer Curve Tracer showed that these two tubes have almost identical values and result in a perfectly matched pair with a deviation of <2%. Can't believe it. It's like "love at first sight"!
Sometimes you just have to be lucky in life. The two tubes are now a "matched pair" until death do them part. Good luck!
With our newly married tube set, we then immediately check the operating point and the output power.
In my preferred setup, I measure the anode voltages, the cathode voltage (for cathode biased amps) and the anode current at the same time. This results in a very clear picture of the operating point. In our case we were very close with a plate dissipation of the EL84's of 9.5W and 9.9W and about 79-82% of the maximum plate dissipation for EL84's in cathode biased mode. That is perfect in this amp!
With a brand new tube set I would probably have lowered the cathode bias resistance a bit to get in the 95-100% range. I don't want to subject the old Valvo tube set to this kind of stress anymore, so that I can keep it in good working order for as long as possible. Let's take it a little bit more "relaxed" (according to the age of the tubes).
Who is now wondering:
"Why do the two EL84s have virtually identical values in the tube test system, but then show slightly different plate dissipation in the real amp?". Even if there is only a minimal 3% difference here.
The answer is: "Life isn't perfect!"
In the test system, the tubes are checked for their technical values under always the same, stable conditions.
In the real amp, however, other factors have an impact on performance. An important factor in a push-pull output stage is, for example, the symmetry of the primary windings of the output transformer. These are almost NEVER absolutely identical.
Thus, even with "perfectly matched" tubes, a slightly different quiescent current flows and the plate dissipation differs slightly. In our case, however, the primary winding halves of the output transformer are really very close to "perfect" with a difference of only 2.2 ohms. I have often measured much larger differences.
What does this almost perfect symmetry of the output stage bring us?
In terms of sound, it remains a matter of taste whether a perfectly symmetrical power amp sounds better or "boring". Some are of the opinion that a slight mismatching results in a more overtone-rich and therefore better sound. I don't want to agree or disagree here. Slightly unbalanced power amplifiers can certainly do "interesting" things in terms of sound.
A factor that cannot be denied, however, is that a very symmetrical push-pull power amplifier achieves maximum suppression of background noise. Especially with regard to mains hum, the effect is used here that the power tubes are connected to the first voltage node with the highest ripple (= residual ripple of the mains voltage), but this is canceled out again by the opposite phase of the power tubes.
And indeed:
In our Philips, the power amp works almost perfectly symmetrically with the perfectly matched tube set and the very symmetrical output transformer, which is reflected in the fact that there is no perceptible mains hum. After switching on the amp, a hum can be heard first, which then disappears almost completely when the power tubes have reached their working point. To be honest, the 1306 is one of the "quietest" amps I've ever heard and has virtually no noticeable mains hum. Astonishing! The blatant opposite are, for example, old AC30's, which ALWAYS have a very clearly perceptible hum due to their untidy design.
In any case, we are in the "more than good" range, and the measured audio RMS output power of 13.1W (before distortion) is also more than healthy for a 12W amplifier.
Sound tuning
there's still something going on.
The amp is now technically in top shape again, with a powerful 2xEL84 power amplifier and extremely little background noise. Great base!
In its original state, the amp is of course designed for linear amplification and therefore sounds a bit dull with the guitar, since we would like to have more high-mids and highs and often a slimmer bass range.
We can reproduce the slimmer bass range perfectly with the "bass controller", which is why it remains in the circuit as it is. It's kind of the reversal of the normal channel of an AC15 or AC30, where the high range can be reduced using the "Cut" control, while the low range is fixed. In the Philips 1306 we will do it in such a way that the high range is fixed and we can reduce the lows with a controller.
So let's turn our attention to the treble response.
Among other possible interventions to push the treble response, the most obvious and simplest intervention is a treble bypass capacitor on the volume pot. We started with a modern 150pF Silver Mica. With this we already get a very nice, crystal-clear upper high range, but we still miss a little punch in the high mids. Swapping it for a modern 250pF Silver Mica gets us in the right direction with exactly the clarity we want, however the sound becomes almost a little too "glassy" and too "HiFi".
Ultimately, our choice is a NOS 250pF Cornell Dubilier "Domino" mica capacitor.
In many other projects we have already noticed that these old "Domino's" (in contrast to the modern types) sound a bit more "moderate". You could describe the sound as "throaty" or "woody", even if a condenser made of mica and plastic can't actually sound like wood... ;-)
In many other amps, the modern mica's are the perfect choice because they sound very classy and almost "hi-fi". We also use these in the 2864-S, for example, and in this circuit they were unbeatable. In the Philips 1306, however, the old Cornell Dubilier brought exactly the timbre that goes perfectly with the somewhat rough EL84. With the selected value, the treble tuning is quite "offensive" (but not "aggressive"), but that's a good thing because, in case of doubt, the treble can be reduced a little using the tone potentiometer on the guitar. Conversely, if there are too few heights, there is no way to regulate them.
To give you a rough idea, we've posted the final schematic below, as well as the simulation of the frequency response with the 250pF treble bypass and various bass control settings.
Cathodyne phase inverter
great work. Fender should come to Hamburg.
As discussed above, the 1306 features a relatively simple, DC-coupled Cathodyne Phase Inverter.
Cathodyne phase inverters can be found, for example, in the legendary Fender Princeton, but in a seemingly "better" version that is AC-coupled and gives the phase inverter's control grid better bias ratios.
Well, what can I say... that's all correct in theory, but in terms of the symmetry of the phase inverter, we got the best results with the existing DC-coupled design. Both in simulation and in practice.
This design is "stressful" for the phase inverter control grid (which has to handle quite a high voltage), but it works perfectly!
So the highly acclaimed Fender engineers from California should spend a night of drinking with the Hamburger Phillips engineers on the Reeperbahn and discuss Cathodyne Phase Inverters. Ok, maybe first discuss the phase inverters, then the Reeperbahn... that probably works better in terms of the order.
Volume pot
unusual or characterful?
With current logarithmic potentiometers, you usually get a control characteristic where the clean range of an amp takes place in settings 1-3, after which we move continuously in the direction of "distortion".
The 500k log potentiometer built into the 1306 seems to have a "flatter" control characteristic. In the range 1-5 we can set the "clean range" very sensitively, while at settings >5 the amp then massively increases the gain and goes into the distortion range.
Whether that's good or bad is a matter of taste. We'll leave the amp this peculiarity for the time being and see how it works in practice. Or not...
Conclusion
The Philips VE1306-02 has become a great guitar amp!
Ingredients that you can hear are certainly the EF40 preamp and 2xEL84 power amp, which are borrowed from a VOX AC15. At the same time, the Cathodyne Phase Inverter and the relatively high "negative bias" are strong Fender ingredients that cannot be denied.
The amp sounds more controlled and less gruff like a VOX AC15, but at the same time has more "bite" like a Fender Princeton due to the EL84's. A great combo!
In the volume potentiometer range 1-5, the volume of the amp can be controlled very sensitively as a bedroom amp and offers the perfect "pedal platform". In addition, it increases the volume significantly and goes into the distortion range. Very cool in terms of sound, but here you need tolerant neighbors... ;-)
Our well-known "Box of Shame" wasn't as full this time as with other amps...
The output transformer, an EL84, some capacitors... that's it!
And really "fancy" is the mains light, which (for a change) is powered by the secondary voltage of the EZ80 rectifier tubes and therefore only comes on when the amp is "ready for use"...