Tremolo not quite right

[dude]

BF Super Reverb tremolo works well but doesn’t come on till 7. Gets deeper on 8, and what you’d expect on 10. But nothing on 3,4,5,6...? I replaced the tube with know good, replaced the roach, caps and check all R’s for trem all good,still the same. Everything else good on the amp.


I was going to replace the pot next, any thing I might have missed.


al

[shooter]

but doesn’t come on till 7

so the roach isn't flashing before 7?
the one I worked on last month trem worked but someone had replaced both ecaps on the cathodes
and the tube was changed, fwiw

[dude]

so the roach isn't flashing before 7?

didn't check, guy has the amp back. I was going to order a new pot but second though, I could have checked the pot
Thanks, al

[PRR]

Sounds like wrong pot taper.

[dude]

Yes, it does. I should have thought this out before posting...

[MFowler]

So the 50K-RA pot and 3M-RA pots?

[dude]

The amp schematic shows a 50K-RA pot (didn't have one in my parts bin), gave the amp back to the owner, when I get it back, I'll check the taper and post if that was the problem. The silver faced Super Reverbs have an on/off switch, this amp has the switch, it's really a silver face that's been blackface inside and the face plate.


al

[sluckey]

The silver faced Super Reverbs have an on/off switch, this amp has the switch

Are you saying this amp has a factory installed switch in the tremolo circuit? I've never seen that. Can you post or provide a link to a schematic that shows such a switch?

There is a popular mod that uses a switch to disconnect the INTENSITY pot. It's not used to control the tremolo. It's purpose is to give a gain boost when the pot is disconnected. Some people will replace the stock 50K-RA pot with a 50K pot with a switch on the back. Very unlikely to find a 50K-RA pot with such a switch. If this is the case that's very likely to be the cause for no trem until 7 on the dial.

so the roach isn't flashing before 7?

The INT pot has no effect on the roach flashing.

[shooter]

I was just replying to

but doesn’t come on till 7

BUT... I did get the pots confused, I was thinking speed since it's "inside" the Osc. 

[dude]

Ok, the amp is my son-in-laws, l now have it there. I know it is a silver face and it has a pot with a switch. The switch is on the back of the pot. I remember looking at both the CBS and BF schematic, the BF had no switch and a 50k R pot, the CBS had a switch on the back and was 50K R no switch, look here at both schematics. This amp has been Black faced but not the tremolo pot. Want pictures?


Maybe the trem pot was replaced but looks all original, if I remember correctly, the switch turns off the tremolo, but just intensity, don’t think so, i’ll  have open it up again,

[sluckey]

I remember looking at both the CBS and BF schematic, the BF had no switch and a 50k R pot, the CBS had a switch on the back and was 50K R no switch, look here at both schematics. This amp has been Black faced but not the tremolo pot. Want pictures?

Pictures of the switch would be great, but the schematic you saw that has the switch would be even better.

[dude]

Ok, I’ll take a look tomorrow for the schematic “ l think l saw?”, open the amp and look again.

[MFowler]

I just put in a push/pull 50K-RA pot in a Super Reverb because it had a switch under the chassis which not practical and it did add some nice gain.


The pot is listed on Rob Robinette website 3 way NFB switching.


Mark

[sluckey]

Thanks for the tip on the pot.

[dude]

Haven’t got to opening the amp yet.
But there is a SPST switch on the back of the pot, it looks original. I take it that this switch turns off the tremolo, taking it out of the circuit which provides more gain? The switch is not a push/ pull like on Rob’s site but turns off when rotated CC. The blackface schematic l looked at does not have this switch but the later CBS does. I believe the SR l have is a 1974 as the speaker codes reveal.  I was going to replace this 50K RA SPST with one without the on/ off. But if being able to take the tremolo out of the circuit creates more gain, l’d want it. Maybe the taper of the pot went south, (I can check) causing tremolo at 7 and above only. Am I understanding this correct?


al

[sluckey]

The blackface schematic l looked at does not have this switch but the later CBS does.

Please show that CBS schematic with the switch. I thought I had looked at ever SR schematic there is, but I guess not, because I have never seen that switch.

[dude]

Ok, the amp has been black faced, l always put a copy of the schematic l use with the amp. The schematic is an early BF, does not have a switch on the pot. But being a novice, l saw the pot with the switch on the back it’s old, looked original but probably isn’t as I too can’t find a schematic with a switch. Like you said it’s an old mod that was done to increase gain and probably was done back in the seventies, as the pot is very old looking. Sorry for the confusion.


You said this is likely the cause of tremolo starting on 7 and above. What did you mean? If the taper checks out ok any suggestions. Just that coming on at 7, it’s pretty deep, can’t get a slight tremolo. Bad pot, regardless if taper checks ok