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.