Tube Amps / Music Electronics
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|2/8/1999 10:06 PM|
||'68 Super Reverb|
New at this and searching for help/answers. Picked up a '68 Super Reverb for $700, in almost mint condition. Had it "blackfaced" ($75). Didn't listen to it much before the mod, but now very bass heavy, no highs, dull, etc. Bright with the bright switch on, but not right that way to my ears. Got Weber's book and checked that all was done right (on the blacfacing). All was save the .002 cap on the reverb input, which I took out. Still like an oak tree. By this time one of the speakers blew. Brought it to another tech. His answer was to change the Sovtec 5881's to Philips 7581's and vibrato side preamp with Ruby 7025
STR and the reverb driver with Ruby 12AX7. He also reconed the bad speaker (that turned out OK)and put in a ground power cord etc. ($285). He said the amp still sounded "deep"(???), but he was sure I would like the change. I don't. It still sounds lifeless. I'm not an expert ear in this, but most of the Fenders I've heard (any) are bright, if anything, and this isn't. I've read about replacing all the tone and output transformer caps with original Spragues, but I know just enough in this area to be dangerous and that may not be the problem. Ken Fischer lives 2 minutes away from me, but a good friend of mine who knows him well says he's still pretty ill and wouldn't even consider calling him on my behalf, so I'm reluctant to do that. Anyone out there have any advice, or am I looking for info. that no one can provide unless they look at the thing? Any advice is appreciated. Thanks
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|2/9/1999 5:31 AM|
I had a 68 SF SR (with Utah ceramic speakers). I did also experience the amp as bass heavy, no highs and so forth. I did the BF mod and some other mods and the amp did sound considerably better, but it also started to oscillate…
This my suggestions – based on my very limited experience:
1.Change all electrolytes.
2.Remove the caps at the power tubes (Restore to BF specs.).
3.Change all brown (chocolate) caps to Orange drops.
(I did change all the ceramics to Silver Mica's as well – but the result was barely audible).
4.Disconnect the vibrato (on/off pot).
5.Plug in a AX7 in the driver position.
6.Remove the V1 tube (the normal channel will no longer work)
7.Swap the Sovtecs for Svetlanas (6L6)
8.Keep the 0.001 microF cap by the driver
9.Change the speakers (not cheap but a major improvement).
10.George L cable between guitar and amp
I’m sure the guys at this BBS have several other good suggestions – but the above mods will IMO improve your tone drastically.
RG Keen at GEO (see resources)
|2/9/1999 6:31 AM|
Mike;This is a good question, and we need lots of answers on this. Alot of people have blackfaced there silverfaced amps. Some turn out great,some don't. For an example, I was working on a couple of princeton reverbs, one was 65 BF/ the other was a 67 silverface. Had them side by side, the silverface sounded good when I first plugged into it, then plugged into the BF,and whoooooo, it blew the SF away. It was louder, it sounded crisp, great breakup[no mush] pulled both chassis, tried to figure this out,I checked voltages, swapped tubes,resistor values,bias,speakers, they were identical in parts inside,I could not figure it out! And the SF sounded good if you didn't have it beside the BF to compare. I see you already spent alot on having this amp gone through, with no success yet. Does your amp use the 5U4 rectifier tube? I found that they sound better with the GZ34. The black face used the GZ34, and some of the SF used the 5U4, The other things are the transformers, sometimes the amp gets too much saturation in the output transformer.And I don't like useing the 12AX7 as a driver tube in this amp. I have seen some Bf Super/R that are stock and sound great, like they are supposed too. I'll bet from what I am hearing you describe, the amp is clean sounds good to about 4 on the volume, then after that mushes outfarts out. There is some changes to the driver circut that will clean it up.But without looking inside your amp it would be hard to say. I know alot of people like to use the amp at the highest clean setting, and use a tube screamer for the overdrive,works pretty good.You may have to have the caps checked to see if they are what they say, and the value is not off. I think some have seen new ones be off quite a bit, and give too much bass,and mush out. There are so many ifs, and I know your tired of spending money, to have no improvement.Maybe Charles[ fender guy] can give his expertise on this, and everyone else. I think we would all like to hear some answers. [Richie]
|2/11/1999 10:03 PM|
I think that Super's can be more finicky than almost any other amp. There, I said it, now please don't flame me!
They just all seem to be very bass heavy, and a lot can sound pretty brittle at low volume with the bright switch on. Personally, I think the 250pfs is too large for the bright switch, but that seems to NOT be the case here.
I'd do a bit of sleuthing. We'll assume that the amp has had all new electrolytics put in. If not.. then Mike should really start there. Check as many resistors as possible without lifing any components, check the tone/couplling caps for leakage (DC), check the bias voltage on the preamp cathodes too. That should uncover anything that's really wrong. If it's more or less correct, Mike may want to go with a silver mica treble cap on each channel. I've found these to be a lot brighter than the ceramic disks that Fender used. Also he might want to change to a silver mica cap on the bright switch (I suppose he'd want to keep the 250pfs, although I like 100pfs better.)
Needless to say, a LOT depends on the speakers and their condition. He may want to try plugging into another set of speaks if possible to see what change there is, or playing another amp thru his speaks for the same reason.
If the amp is just too bassy - getting farty - then you can usually solve it by using a smaller cap at the input of the phase inverter. I prefer .001 to limit the bass a little, but 500pfs may not be a bad choice, depending on the speakers.
|2/9/1999 8:49 AM|
Depending upon what part of the year your '68 SR was built, it either was already a blackface circuit (AB763 schematic) or VERY CLOSE to a blackface circuit. (Although some '68 Fenders do have an AWFUL-sounding fixed/cathode-bias combination circuit on the output tubes which MUST be rewired as fixed-bias only before the amp ever has a prayer of sounding good.)
What your amp REALLY needs is to have an electronic restoration done, if this has not been done yet. Someone needs to go in there and replace ALL the electrolytic caps, as well as any other components that have gone bad or drifted in value. Also, all pots, jacks, and switches need to be tightened. All pots should be cleaned. Loose ground connections should be fixed. Tube sockets may need cleaning and retensioning.
I would be very wary of techs that try to solve most problems by selling you new (and sometimes expensive) tubes. The best tubes in the world won't make your amp sound right if there are gremlins INSIDE the chassis! There is no reason why your amp shouldn't sound great. But you may need to find a tech that has the patience and skill to make this happen. Try getting some recommendations from pro players in your area.
|2/11/1999 3:44 PM|
for what its worth - follow Jim's advice- and DO NOT get Torres's book . if you want that unique Blackface SR sound - then find a compotent tech - not a "i got a soldering iron and some parts" tech but someone who has experience, at least some formal/or self-taught education in electronics, power supplies, transformers etc .. AND how all od these items work together to make a great musical amplifier .. Torres and Weber et al .. IMHO have provided a nice set of schematics and much food for thought asbout guitar amps but for a novice I feel that their "tips and trcks and hot-rod mods" are nothing more than a collection of opinions and perhaps some trial and error results .... so that said have you thriughly- using an accurate schematic AND layout verified that your SF is accurately wired as a BF? Are ALL component values and type (mylar/ecectro/ceramic etc ... ) completely accurate? Also I have heard that the Jensen 'vintage' re-issue 10" speakers sound great in SR's.
|2/9/1999 2:03 PM|
Sounds to me like a cap problem. You should replace all the cathode bypass caps in the preamp, and check the filter caps for visible bubbles while you're at it. You should really change them too. 30 years is a long time. Changing all those brown rabbit turds to orange drops or better I would say is a must-do. One of them could have drifted and would throw it way off. Is the normal channel also bassy? If so, be sure to replace the coupling caps. If you're game to change some values, try lowering the value of the coupling caps from maybe .02 to .002 or ,01 to .001. You can try changing all the .1 and .047s in the preamp to .02s. That's a mod your friend Ken Fischer suggested in the Tube Amp book. I think he also suggested changing the ceramics to silver micas. Not for less bass though, but for cleaner mids and highs. If you still need to cut bass try changing the .1s in the driver circuit to .02s. Thats what Marshall uses in the 1987, and I think some others too. I agree with a lot of what was said already. New Sovtek 5881s are fine and probably at most cost 1/3 as much as NOS. The 12AX7WXBs and WXTs are fine also. You should be happy with the basic sound before expecting a change from 12AT7 to 12AX7s for the reverb and power tube drivers to make any difference. If your amp is in good shape, it will sound fine have no trouble with Sovteks. If your speakers are original and aren't blown or havn't been torn or gotten wet, they should be fine also.
Finally...I'm no expert, but I do know a little about it and If I had to do a quick and dirty fix, the first place I'd look is at the coupling caps between the preamp stages and into the driver. Then the electrolytics, then the tone caps.
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