BF Deluxe Reverb V5 voltages

[Telenut62]

I have just wired in a new ClassicTone PT with lower secondary volts to bring the amp more inline with original voltages. I have been going through a pre-start check and with B+ at 435V things are not too bad, just about 10V or so above spec..V1,V2,V4 are about 180V on the plates and 1.5v on the cathodes..
V3 is 420v on the plates 7.5v on the cathodes..V6 is a bit high at 199V/196V on the plates and 85v on the cathodes. However V5 the vibrato tube is 414V pin 1 and 368v on pin 6...pin 1 is way over spec it should be 270V. The cathodes are near 0V. Is this normal as I seem to remember reading about the vibrato tube having higher plate voltages as there's no signal. It looks to me that the filter cap B voltage is going straight into the plate via the 220K resistor (no voltage drop) and the optoisolator, so is there a prob with these components? I'll do a sound check next to see how it all sounds. I did change the V5 tube and it made no difference to the voltages.

[Telenut62]

Sound check revealed low volume output....grrr But I did discover I have no ground lead on the resistor leg of the opto, it wasn't on the drawing supplied by Mojotone...thank you guys!!

Stay Tuned!

[Telenut62]

Well I have made progress, the low volume was the speaker cable..doh! So when I fixed that it all seemed to work, I can hopefully start tidying up little issues like better shielding and the vibrato channel....motorboating when I turn up the intensity etc etc.

[andyfromdenver]

Originally Posted by Telenut62

Well I have made progress, the low volume was the speaker cable..doh! So when I fixed that it all seemed to work, I can hopefully start tidying up little issues like better shielding and the vibrato channel....motorboating when I turn up the intensity etc etc.

Oh gawd I hate that motorboat sound!!
We're trying to rid an old Gregory Apollo of it.
That amp is weird, a lot of wires are bundled up with the heaters and are at least 8" too long. I've been tasked with lead dress. I think it will take something else to rid the motorboat sound. I have a feeling I'll go in today and it will be fixed.

[Telenut62]

I have been reading up on this trem circuit and how a Optoisolator (LDR) works and what causes it to not work, all new stuff to me. So my problem with motorboating can be caused by several things....lead dress, DC leakage, faulty components. First of all when I activated the Vibrato footswitch the voltages on V5 came into line...as I read here..

The trem circuit has two triodes - the oscillator and the output buffer. When the trem is off, that connection to the bias supply puts like -40v on the grid of the oscillator triode. That is more than enough to cut the tube off, so when it can't conduct, the full B+ supply voltage will appear at its plate. That is normal.

The clues with the motorboating are...

It is only affected by the intensity pot and the reverb pot, noise level increases when the reverb is turned up (reverb tank is not connected yet) Volume pots have no effect, which is good. The LED is flashing as soon as I turn on the footswitch. There is practically no DC leakage at the intensity pot or the 25uf caps. All the components are new so I'd be surprised if it was a component at fault. So I'm hoping it is a lead dress issue.....

It might be worth mentioning also that the only other hum/noise issue is that when I bring the pickups real close to the bias circuit corner there is a dramatic increase in hum.

[Telenut62]

Ok prob seems to be solved by moving the 25uf bias circuit cap ground to a lug on it's on, away from the PT shared centre taps tag strip. Now to hook up the reverb tank