Questions re ~1976 Twin Reverb/trashy distortion

[Steve S]

My first post on forum - I guess some post has to be the first.

Anyway, I'm trying to find out about something about my Twin Reverb. It is a silverface w/pullout master volume which I believe is about a 1976 vintage. I've had it since early '80s, never serviced it or thought much about servicing it. It's all original as far as I can tell except the power tubes - they're all 6L6s but 3 are Philips and 1 is labelled "International C Servicemaster". I'm ashamed to admit I never noticed the tube mismatch until very recently, unless somebody has switched them on me - unlikely. My current problem with this amp is trashy distortion at relatively low volumes.

I plugged in a separate speaker cabinet and did not hear the same trash, so I suspect the speakers rather than the tubes/caps/etc. The trash with internal speakers comes out of both speakers. (I also have a quad set of $1 garage sale 6L6 tubes which don't seem to make any difference in the distorted sound).

1) Original speakers have several codes stamped on them: 513625, 3747619 and 005379. I'm guessing that the 3747619 is the manufacturer/date code - mfr. 374, 19th week of 1976. However, 374 doesn't seem to correspond with any EIA code that I can find. Any ideas, or have I completely misread the codes?

2) Plugged outboard speaker cabinet into Ext Speaker jack (on the right as you face the rear panel) but just got low level distorted sound. The tubes glow blue at max volume with guitar input but only low level overloaded sound comes out (this also happened when I plugged the internal speakers into the Ext Speaker jack). Plugged outboard cabinet into the regular speaker jack (on the left) and got regular volume/tone. I am plugging in an 8 ohm EV Force 12" speaker to the 4 ohm output. Don't know the power rating of the speaker but I think it's about 100W.

3) When I have the internal speakers _and_ the outboard speaker plugged in I get the trashy distortion out of both sets of speakers

So, after reading back through this stuff, I believe I'm trying to ask these questions:

Can anyone tell me the original brand of speakers, and are they worth reconing?
Why does plugging something in to the Ext Speaker jack give me distorted sound (except when I keep the internals plugged into the main jack and the outboard 8 ohm into the external jack, when I get reasonable sound from both)?
Why would I get trashy distortion from _both_ internal speakers but not the outboard speaker unless I have all plugged in at the same time?

Thanks!

Steve

[Enzo]

You must always have something plugged into the main speaker jack first. it has a shorting contact. If you plug ONLY into the external spkr jack, then that short remains across the output. That is why the speakers sound low level and distorted.

Plug your external cab into the main speaker jack in place of the internal speakers. NOW how do they sound? That will be the sound of the amp, good or bad. If the amp sounds OK through good speakers, then your old speakers are bad.

When a number of speakers are all wired together - as they are when all connected to the amp - they can interact. If the voice coil is rubbing the gap wall, this can short out the amp signal and then all the speakers will get the crappy sound.

isolate the problem to the amp or the speakers, then we continue from there.

[Steve S]

Questions re ~1976 Twin Reverb/trashy distortion

Plug your external cab into the main speaker jack in place of the internal speakers. NOW how do they sound? That will be the sound of the amp, good or bad. If the amp sounds OK through good speakers, then your old speakers are bad.

Enzo, thanks for the response. I'm in Ann Arbor, not too far from where you are.

Anyway, yes, the amp sounds OK with the outboard cabinet plugged into the primary speaker jack. So, perhaps the question is are these particular stock speakers worth a recone (maybe just one of them) or is it a better $$/sound investment to replace?

Thanks,
Steve

[acorkos]

Not sure what your original speakers are, but if you decide to replace them, the Eminence Patriot 'Red, White & Blues' are great sounding speakers in your amp.

[Steve S]

Not sure what your original speakers are, but if you decide to replace them, the Eminence Patriot 'Red, White & Blues' are great sounding speakers in your amp.

Not sure what the originals are. They have the Fender label, and the codes stamped on them are 513625, 3747619 and 005379. I can't identify an EIA code in any of these, though I think it's 374, with 7619 indicating year/week of build.

Steve

[Steve S]

Ahh... they are Cletron speakers, made by the Cleveland Electronics Company. Anybody know this brand and how they would have come to be installed in a Twin Reverb? They have the Fender sticker on the back and the date code 3747619 (19th week or 1976) is consistent with the 1975/1976 date codes on the Schumacher transformers, so they look to me like a factory install. I never heard of these speakers before, but somebody pointed me to a mfr. code list at
http://www.provide.net/~cfh/pots.html.

Steve

[Regis]

Ahh... they are Cletron speakers, made by the Cleveland Electronics Company. Anybody know this brand and how they would have come to be installed in a Twin Reverb? They have the Fender sticker on the back and the date code 3747619 (19th week or 1976) is consistent with the 1975/1976 date codes on the Schumacher transformers, so they look to me like a factory install. I never heard of these speakers before, but somebody pointed me to a mfr. code list at
http://www.provide.net/~cfh/pots.html.

Steve

Ted Weber would probably recone them, and you can specify some of the details about the recone such as doping, etc. Also Orange County Speakers in CA would do it too, I've had speakers reconed from both of them and they both do a good job. It would probably be about $50-$60 per speaker plus shipping to recone them.

You should probably take the amp to a qualified tech, (drive up and see Enzo!) to have the amp gone over. New tubes, maybe a recap, anything else that needs fixing. The amp would be good to go for years after all that.

Good Luck,

Regis

[Steve S]

Well, I sort of take it back about things being nice and clean with the outboard speaker cabinet plugged in (it's 8 ohms plugged into the 4 ohm jack, if that makes a difference). I still get some trashy distortion at moderate levels - sounds great a low levels but if I push it then it breaks up with radio-static-quality distortion on top of the signal. This is for either guitar or Rhodes input, so it's not coming from the instrument.

Anybody have thoughts about what in particular to investigate from here? Next time I get a chance I'm going to swap some tubes around see how much, if any, is related to having the reverb on or not. Also, all this has been with inputs into the reverb channel so I'll also check the straight channel, too.

Thanks,
Steve

[Mark Black]

I just worked on one of those amps and it had (among other problems) a tired & sagging reverb tank that caused a similar-sounding distortion. One of the springs was sagging enough that the ferrite beads were rubbing on the transducer armatures...

[drlowlow]

You mentioned that you never had it serviced and although it is possible to get it sounding better from advice from this forum I think there will be other problems that wont allow this amp to sound its best until it it has really been gone over by someone with some experience. I don't recall you ever mentioning biasing it when you changed your tubes and that could cause distortion. It just an accepted fact of vaccuum tube technology that components go out of tolerences and need attention at certain intervals.

It should be safe with the impedence mismatch although it will change the frequency response a bit.

The speaker question is up to you really. There are some businesses out there that can do a fine job with a recone but there are also some businesses out there that build speakers that might subjectively be better suited for you.

If you want to troubleshoot this yourself start by checking if it isn't the reverb channel and then check the bias (if you haven't allready). If that doesn't do it than start looking at the powersupply.

I can tell you that if you don't have much experience with this and you want the amplifier working its best quickly then your best bet is as I already stated to take it to someone with experience that can find all that is wrong with it replace what it needs and get it back to you.

[Bruce / Mission Amps]

Is that one of those amps with the crazy, impedance jumping, transfer jacks in the back panel?

[Steve S]

Is that one of those amps with the crazy, impedance jumping, transfer jacks in the back panel?

The only jacks other than the reverb in/out are the main and external speaker jacks. Is that what you mean? It looks all original to me.

Steve