New to Ampegs

[Dave1966]

Hi all,

I am a newbie to Ampegs, but I have built a couple of Fender clones (Deluxe and Champ), which both went well and I am currently building a Vibroverb.

I have just taken ownership of a R-12-R 1963, with the 6SL7, 6SN7, 6V6GT and 5Y3 configuration. The tremolo is not working, but everything else is all ok. Two caps have been replaced fairly recently in the reverb section by the looks of it, but it is otherwise stock, including 3 x original Ampeg badged Sylvanaia tubes. The rest are old (not dated) RCA's.

I have looked at the schematic and I am struggling to understand where the signal enters the tremolo section. Can somebody explain the tremolo section, I am used to a separate channel, as used in Fenders.

I am loving this amp, but really want to get the tremolo up to speed so to speak.

Many thanks

Dave

[Hangman]

The tremolo in the r-12R is a bias modulation type as i recall. The guitar signal never really "goes through" the circuit, The tremolo oscillator just oscillates the bias voltage, much like it does in the fender deluxe.
If you are not getting tremolo, it's possible that the oscillator isn't working. That amp should have a foot switch though, Maybe the foot switch is bad?

[Dave1966]

The tremolo in the r-12R is a bias modulation type as i recall. The guitar signal never really "goes through" the circuit, The tremolo oscillator just oscillates the bias voltage, much like it does in the fender deluxe.
If you are not getting tremolo, it's possible that the oscillator isn't working. That amp should have a foot switch though, Maybe the foot switch is bad?

Thanks Hangman. I was thinking in terms of the Fender Vibrato, which is a separate channel of course......doh!

You are correct regarding the bias modulation and I will be checking it out this weekend. I have a few spare caps and resistors kicking about, so should get it running fairly easily....famous last words?

Thanks again

Regards

Dave

[Hangman]

Check the foot switch too. The circuit needs to be grounded through the switch, if the cable is damaged or switch bad, that could be it.
Did you try swapping tubes? Could just be a bad section of one of the 6sl7s.

[Dave1966]

Check the foot switch too. The circuit needs to be grounded through the switch, if the cable is damaged or switch bad, that could be it.
Did you try swapping tubes? Could just be a bad section of one of the 6sl7s.

I got the amp yesterday and took it straight to a jam night to show my mates. I have not had a chance to do much to it physically, but I do like to pre prepare. The previous owner did inform me that he had checked the tube. I have looked at the cable to the footswitch and can see there is some damage to it, where it enters the chassis. I will get my meter out on Sunday and do some checking. I will let you know how it goes.

Many thanks for the speedy response, it really is appreciated!

Regards

Dave

[Dave1966]

I have tested the FS to death, its definately OK, as is the cable although it looks very much the worst for wear. I have also tested all the caps, resistors and pots. Swapped the tubes as I dont have spares. No change. Maybe the caps read ok, but are "weak"? I get avery slight effect for a split second when throwing the switch, but it goes away immediately. I don't have any voltages on the schematic, what should I expect on the "B" node?

Thanks again for your help!
Regards

Dave

[Hangman]

Pretty hard to test caps reliably. They could be testing ok but leaking DC at high voltages. If that section hasn't been recapped, I would do it.

[Dave1966]

I have ordered all the caps for that section. I have ordered Mallorys, I guess they will be ok. I was going to use orange drops because I had a few, but space is very tight.

[Hangman]

the Mallorys are great caps. probably more similar to what was originally in there.

[Dave1966]

Siemens 6sn7 WGTA, any love?

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the Mallorys are great caps. probably more similar to what was originally in there.

Thanks Hangman, I reckon the Spragues would have been plain ugly!