__Univox 1221.....Problems with Reverb & Trem

[AXEnGEAR4J]

Just picked up Univox 1221 head and 2X12 matching cab for kicks. The seller said the reverb and tremelo were working prior to shipping. Neither one worked upon arrival.

Checked all the obvious areas of wiring, tubes etc.
Anyone with experience on these and maybe what to look for next and where to start?

 

[epluribus]

Uh-oh...yes I have one and no I don't have much actual experience with the problem. Last time my FX quit it was a tube issue, and that was back about 1975.

Kinda strange that both would suddenly fail at the same time. In fact, highly unlikely. Does your number one channel work at all? If so, then either something very strange has simultaneously happened to a very isolated segment of the two seperate FX circuits or the amp's been tampered with.

The easiest place to look would be the footswitch jacks. Your FX are supposed to work without the foot switch at all, but it's possible somebody trashed the male jacks tripping over the cord and left the stubs in the holes. I knew a guy who did this to another amp, but same concept. Difficult and violent, but busting the jacks can be done. Anyhoo, this would kill the FX cold, but the channel would still work.

From there you're into pulling the chassis. (If you don't know how to do this, STOP HERE. Get somebody to show you how to do this safely. Fatal voltages inside.)

Since it's both FX, IMHO the amp's probably been hacked. Chances are somebody bungled a very common mod on these things...connecting the FX to both channels. Both the Reverb and the Trem exit and re-enter the signal path at one point--right after the tone pot. If they tried to hot-wire the FX and ended up killing 'em both, I'd look at that shared connection for problems. (Incidentally, the reverb secondarily exits the signal path in front of the tone pot as well, but if they messed that connection up, the trem would still work.) I haven't done the mod myself and know little about it, but a little googling will take you to a schematic. I'd post a link if I could remember where I've seen it. Anyhoo, that's a likely culprit.

On to the nitty gritty. I gather from your post that you show heat in all of your tubes--that's a good sign. One of your 6AN8s, a 12AX7 (both sides), and your entire 12AU7 are used for FX. Not likely they'd all fail at once without taking down lots of other things--more likely somebody trashed the power supply either to the heat or B+.

So if Channel One works dry, and the switches are good, and you have heat, then you're going to be measuring voltages on all the relevant tube pins to confirm that the FX tubes are working. Finding the problem on the hot side is very unlikely, since the tamperer would have to damage the B+ at several points on the power rail, or individually disable both signal paths. About the only easy place to kill both FX is if they share a common ground at some point, and the ground has been lifted. That one I can't tell you.

IMHO, since it's both FX, that narrows it down substantially. If it's not tubes, it's tampering with a shared point in both circuits, and that's right after the tone pot. Let us know what you find out, and if you open 'er up, be careful.

--Ray

ps...you tried sticking a grunge pedal and a good EQ in front of one of these? Kick the bass up, downtune the guitar, and see what you find...

 

[AXEnGEAR4J]

Hey thanks for the input.

I've taken the chassis out and looked in it, don't see any mods, hacks or broken jacks etc.. actually it looks pretty clean and untouched. All the tubes show heat however the 6AN8 appears a little dim however dunno if it's bad. The previous owener said he once remebered the reverb/trem not working and he had to wiggle one of the tubes and then it worked. From that I suspect a dirty or faulty socket. I did clean them with contact cleaner with no change, I guess the next thing would be to test the pin connections and test the tubes.

I bought this off the bay, here's the link:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170303771916&ssPageName=ADME:X:RTQ:US:1123http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170303771916&ssPageName=ADME:X:RTQ:US:1123

 

[epluribus]

V4 doesn't seem to look too bright in the pic. Can't recall, but that might be your second 12AX7, which does indeed sit in both FX circuits. If it's not getting heat, that could be your problem. If wiggling the tube helped, that could either be a pin socket (4, 5, or 9 IIRC) that needs re-tensioned or it has a cold/intermittent joint. (Or a dead heater, but you said your rolled the tubes, so doubtful.) Do you know how to measure the voltages on the pins? That could tell you quick...but above all, be safe.

--Ray

 

[AXEnGEAR4J]

Yes I plan to go back and check connections however I'm not experienced on how to measure voltages, its time I learn these things as I have quite a few vintage valve amps. I tried to do a search but didn't come up with anything. I understand about voltage safety and type of person that has built everything from races cars to houses and intalled electrical circuits and wiring so I'm not afraid to tackle. Any recommendations?

 

[epluribus]

Yeah, as a matter of fact...check this thread out. This is the one where John Phillips explained this to me in dummyspeak the first time I tried it. A little long, but worked like a champ, been using the techniques ever since. SGW: addictive.

--Ray