Blackfacing a Silverface Super Reverb for more natural overdrive.

[Tele5015]

Hello I have a 1969 Super Reverb and it stays clean all up the volume knob There is not even a hint of overdrive. I went to Elderly instruments the other day and they had an all original 1965 Super Reverb not a reissue. I played it and it got tons of natural overdrive and it sounded killer. So I was wondering if I had my Super Reverb blackfaced if it would get natural overdrive.

 

[sds1]

Your amp maybe just needs general servicing because it should break up, compress, feed back, do all that nasty stuff you expect from volume 5 on up.

 

[Tele5015]

Your amp maybe just needs general servicing because it should break up, compress, feed back, do all that nasty stuff you expect from volume 5 on up.

It was just serviced and it sounds killer it just has the silverface curcuit thats doesn't overdrive that much.

 

[Old Tele man]

Check the tubes...are they all original and correct?

 

[BelindasShadow]

It was just serviced and it sounds killer it just has the silverface curcuit thats doesn't overdrive that much.

I have a ‘71 silverface Super Reverb which overdrives naturally, so they can definitely do it!

 

[JD0x0]

My 74? barked pretty good. I don't think most people even understand what 'blackfacing' is and how little was changed in some of the amps.


http://acruhl.freeshell.org/mga/main/sf_bf_mod.html

"uppresser caps: Fender added .002uf (or sometimes 1200pf) capacitors to the grids of the power tubes (pin 5). These bleed off frequencies that they thought were too high to be heard with guitar. The effect of these is to bleed off any frequencies that the amp will oscillate at. Oscillation is like feedback with a microphone. It feeds itself and runs away from you if you don't do something about it. Amps can do this internally, and it's a big problem. For you tech types, somebody emailed me and said that the effect of these caps is -18 dB at 6 kHz! Ouch! The caps are actually a good idea, but they tend to bleed of high end "sparkle" from the amp. These caps were added because of problems with the lead dress that was causing the amps to oscillate. It's unfortunate that Fender needed these. The best way to control oscillation is to design the amp not to oscillate in the first place! But for cost cutting's sake, it was cheaper to put these caps in than spend the extra labor to make the amp more stable. These caps can usually be removed and the amp will run fine. I haven't run across an amp yet that started oscillating without them. But, I have heard from some techs that have seen many amps that can't live without these caps. Oscillation suppression is nothing new in Fenders. Tweed bassmans had a cap across the plates of the phase inverter to help with this (47pf). If your amp plays fine after the mod and then all of a sudden acts like it looses most of it's power, it is probably oscillating. Try the 47pf cap like the tweed Bassman and see if that fixes it (look in schematics to see how it is done). There is also a much rarer oscillation suppression method Fender had, it involved a .02 cap and a 220k resistor going from one leg of the power section then held 100 ohms above ground via the feedback loop. This is rare and only occurred in the early 70's.

Phase inverter: Fender changed the phase inverter in a few ways. Starting from one end and going to the other: The coupling cap increased from .001 to .01. This has the effect of letting more bass through to the power section. This sounds like a good idea, but to my ear makes the bass get overbearing. The .001 cap sounds tighter with more defined bass to me. After that, Fender used 330k resistors on the grids of the phase inverter instead of 1 meg. The cathode resistor on the phase inverter was made smaller which ran this tube a little hotter. The plate load resistors were decreased from 82 and 100k to 47k. This reduces gain. Overall, the changes to the phase inverter look like they were designed to tame the amp and change the way the amp sounds to what Fender wanted at the time.

Reverb circuit: Fender tended to run the reverb driver tube very hot in the silverface years. Blackface amps came with 2.2k resistors bypassed with a 25uf-25v electrolytic cap. Sometime in the 70's, they started to change this value. I've seen 1.5k, 820 and 680 ohm resistors here without a bypass cap. Fender also added a cap from the plates of the reverb driver to the cathode. They added a cap to ground after the reverb tank as well. I've found that I sometimes like the silverface method for reverb better than blackface, but I do take out the added caps to ground. I will leave the amp otherwise stock if the reverb sounds good to the owner.

Bias supply: Fender changed the bias supply from a level to a balance control. The balance control allows the tech to match the tubes, but not set the bias level which is what can determine tone. Also, some extra filtering was added to the circuit (two 70uf-100v's? Don't remember exactly). I always change the bias supply to blackface specs because we use matched tubes these days! When replacing the bias supply filter caps, I usually just use one 100uf-100v. "


None of these listed mods would change the amount of overdrive, significantly, IMO. Changing the grid leaks to 1M from 330k will give a slight increase in signal to the power amp when the amp is cranked hard, but that's about it.


Got any gut shots of your amp? Sometimes when they're 'serviced' ONLY the Filter caps in the power section are changed. The cathode bypass caps are often neglected and if they start to go bad you WILL lose gain.

 

[Dacious]

Hello I have a 1969 Super Reverb and it stays clean all up the volume knob There is not even a hint of overdrive. I went to Elderly instruments the other day and they had an all original 1965 Super Reverb not a reissue. I played it and it got tons of natural overdrive and it sounded killer. So I was wondering if I had my Super Reverb blackfaced if it would get natural overdrive.

You need to get your amp rebiased, and check what tubes you have where. There's stuff all diff between BF and early SF SRs. I'd bet you have a 12AT7 where there should be a 12AX7

 

[sds1]

It was just serviced and it sounds killer it just has the silverface curcuit thats doesn't overdrive that much.

Silverfaces are not notorious for being clean like you think, your amp is just missing something. This is good news, if it sounds killer... then like others above have suggested it's probably a lower gain tube or something simple.

 

[BobbyZ]

Check the voltages. As I recall there were a few silverface SR circuits with lower voltage. They did that with SFTRs too.
Hopefully it's just something minor like the other guys said, like bias.