 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.191.48.48
ok, this is a guitar amp. Sorry about that, but I've yet to find a forum with this level of technical expertise in one of the guitar communities.My questions are at the bottom, but first here's the situation:
I have a Fender Super 112 guitar (tube) amp. It's 1990 vintage and except for newly installed tubes I believe it's all original parts. The problem is output (loudness) is pretty weak. On the clean channel, volume is too low to fill a small room, even with volume pot cranked up to max. On the O/D channel, it can be loud, but I'm sure it's not putting out what it should. It sounds ok, but it's hard to say it sounds as it should. It has new power tubes (6L6GC SVETLANA), and the preamp tubes are good (2 - 12AX7A; 1 - 12AT7) Tubes all test good, and I've tried other tubes too.I'm trying to decide if I should put money into this amp, and how much it's likely to cost. Questions -
- Can anyone suggest what is the likely cause(s) of the low volume level?
- Fender's web site says this is a "fixed bias" amp. Does that mean it's not adjustable, even by a tech? Or does that need to be set before I put any time on these new tubes? (I've had it open and there are no pots on the circuit board)
- I plan to re-Cap it, and check/replace resistors. Any other service that should be done to restore it to original sonics? Will these parts likely solve the volume level problem?I'm going to get a quote to have the amp refurbed, but am also considering DIY restoration. Any advice is greatly appreciated.
Follow Ups:
There could be any number of things causing a drop in output.Why did you replace the power tubes? If one of the old tubes shorted
and lost bias you could have a burned up screen resistor and also a scorched tube socket, and simply throwing in a new pair of tubes won't solve the problem.There is both adjustable fixed bias and non-adjustable fixed bias, but both bias methods ARE adjustable if you know what you are doing.
Having the new tubes properly biased may or may not solve the problem. Earlier this year I went through three sets of Winged C 6L6GC's that were supposedly matched, all three sets were out by at least 10 mA and one set was out by 24 mA, and these came from a reputable dealer. I'm now running TAD's and am very happy with them.If you have the time and desire to learn tube amp repair, this would be a good way for you to get your feet wet, but first you need to know how a tube amp works before you can diagnose problems. Please don't start digging inside the amp until you have some basic knowledge about how to discharge filter caps, Fender amps can store over 500 volts of D.C. and people can and do die by not knowing what they are messing with.
My advice is to take it to a tech., it can probably be repaired for under $50.
thanks for the detailed reply Greg. You've hit on multiple relevant points for me.1) the reason I posted here is I am trying to learn tub amp repair. I have limited experience with SS amps, and with an old Fisher X-202 integrated. I'm far from competent however. I'm trying to decide if this is is the amp to learn on, or perhaps building a tube kit is a better way. I do understand the basics of tube operation, danger and discharging caps, etc. Suggestions?
2) As for why I replaced the tubes - one was indeed shorted. So I've done something stupid, and my new tubes indeed test bad now. At least they weren't expensive - so I'll call it a cheap lesson. I had the amp opened up (before replacing the tubes) and nothing obviously is scorched.
3) I've traded emails with a local tech that repairs and mods guitar amps. I'm calling him today to set up an appointment. My budget for repairing this particular amp is open, but I'm not sure this unit is worth dropping a lot of $ into it, as opposed to cutting my losses and buying a new one. My thought is while I have it in the shop I should recap it. I have no idea what that will cost, but my decision will depend on his estimate for the full job.
thanks again . . .
1)I'm not familiar with your amp but suspect that since it was made in 1990 that it is a circuit board design and not really an ideal amp to learn on, a much better amp would be one with P to P wiring.Since your amp only has three preamp tubes I'm thinking it must be some sort of hybrid design, but without seeing the schematic I'm only guessing. Building an amp from a kit is a great way to learn about tube amps, but be sure you get a kit with detailed instructions. Allenamps.com offer this kind of kit but are higher priced than some of the other kits offered due to the fact that he uses top quality components in his kits. Webervst.com also has quite a few amp kits but are geared more towards people who already have an understanding of kit construction and you only get a schematic and wiring diagram with it, no detailed instructions. There are quite a few good books and DVD's out there. I can reccomend the Gerald Weber DVD's and books and also Lee Jackson has a series of DVD's out but I haven't seen them yet.2)If you installed the new tubes and one or both of them fried, the first place to look for trouble is in the bias supply circuit, hopefully the problem isn't the power transformer. Since you didn't see a pot when you looked at the chassis I'd say it is an non-adjustable fixed bias control, this means that bias is set by finding the right resistor value to supply the proper bias voltage.
You could have a tech convert this to adjustable but not sure it would be worth it.3)At seventeen years old it would be a good idea to replace all the elctrolytic caps as preventative maintenance but I've seen caps last much longer without going bad. So if you plan on keeping it, go ahead ang get the cap job done, or skip the cap job, sell the amp and buy a kit.
Good Luck
Greg
thanks again for the advice Greg. I spoke with the tech today and have decided to have him fix this one. Among other things, this amp is hard to work on becaus eit's not really designed with service in mind. I'll find another to learn on, and in the mean time, I have many other projects to consume my free time . . .I'm going to look into the kits you suggest.
| ||||||||||||
| ||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
