vintage Univox U65rn fix? light turns on, but no sound...

[randmcnasty]

Hello everyone,

I just received a vintage Univox U65rn guitar amplifier in the mail today that I got from Shopgoodwill.com. To my disappointment it does not work, but I was hoping maybe there was some way that I could fix it??? I have never worked on a guitar amplifier before but I do some DIY electronics and stuff, so I know how to solder... that's all battery powered stuff though, so I'm also wondering about any safety precautions I would need to take before working on this amp so I don't get zapped.

So, the amp is from the early 70's, I believe... and not in the best shape. It's dirty, missing a knob, the pots feel scratchy, and there is no sound. I plugged it in and turned it on and instantly thought something was wrong when I didn't hear that "pop" sound you usually hear when turning on an amplifier. Sure enough, when I plugged in my electric guitar I got nothing. I tried all 3 inputs, and got no sound at all. The power light does come on.

One thing I noticed is that it looks like perhaps the speaker was replaced at some point because the wires coming of of it are connected (twisted together, not even soldered... exposed wires) to the original wires coming out of the amp!

Any ideas? I joined this forum today so I could get some help from the community here, thank you.

[52 Bill]

Welcome to the place.

The first step would be to search on-line and see if you can find a schematic for your amp. If you find one, post it here and we can all communicate on the same level as we try and guide you.

The first thing that I would suggest is to test the speaker. As it has been messed with already, it may or may not be a good clue as to what is wrong with the amp. The quick and dirty test would be to disconnect the wires from the amp that connect the speaker. Next take a 9 volt battery and touch it to the two terminals on the speaker where the wires were connected. If the speaker is working you should hear a pop from the speaker. If you don't hear the pop, then there may be a problem with it.

Good luck.

[randmcnasty]

Thanks for the tip! Did the battery test and no pop... upon closer inspection I found that the smaller wires coming off the speaker's terminals and going to the speaker cone have broken... 1 is broken at the joint and the other tore off at the cone, looks like there's a tear in the paper, too.

So, I guess now what I would need to do is find a proper replacement speaker???

[52 Bill]

Thanks for the tip! Did the battery test and no pop... upon closer inspection I found that the smaller wires coming off the speaker's terminals and going to the speaker cone have broken... 1 is broken at the joint and the other tore off at the cone, looks like there's a tear in the paper, too.

So, I guess now what I would need to do is find a proper replacement speaker???

You might be able to fix the lead wires and patch the cone, but a replacement would be easier.

You might want to test the amp with a different speaker to see if it is working or not before you get a new speaker. If the amp is dead or not working correctly, the overall repair cost might be a consideration.

[nickb]

Schematic >> here <<

Have fun and stay safe

[randmcnasty]

All I had was a tiny (like 2 or 3 inch, 8 ohm) speaker, but I hooked it up and it worked!

I don't know very much about speakers, I think the u65rn has a 15", 15 watt speaker (???)

Wondering how I go about finding a proper replacement speaker... I would like to use the amp with a bass guitar.... thinking about stopping by the old science surplus store tomorrow, I know they have some speakers there, but I'm not sure how big.

[52 Bill]

I don't know very much about speakers, I think the u65rn has a 15", 15 watt speaker (???)

The web sez that the amp has a 12" speaker. The schematic sez that it should be a 4 ohm speaker. I would think that a 20-25 watt rating would be fine.

You need to measure the speaker that is in there to know the diameter for certain. A 12" will measure slightly larger than 12" across the metal frame.

[J M Fahey]

All I had was a tiny (like 2 or 3 inch, 8 ohm) speaker, but I hooked it up and it worked!

I don't know very much about speakers, I think the u65rn has a 15", 15 watt speaker (???)

Wondering how I go about finding a proper replacement speaker... I would like to use the amp with a bass guitar.... thinking about stopping by the old science surplus store tomorrow, I know they have some speakers there, but I'm not sure how big.

You shouldn't put *any* random speaker there or ypu'll be very disappointed.
You need a proper *guitar* type one.

Musicians, being bthe delicate insecure creatures they are (he he, just kidding ) spend their lives constantly changing gear in the hope it will give them that magic touch, so buy/sell/trade/mod stuff all the time.

One very popular (and in fact useful) "mod" is changing speakers, specially (perfectly good) original factory ones for others of perceived higher value, then sell the original ones for peanuts ( since "nobody wants them" ).

Search local Craigslist so you don't waste time on shipping (will use some gas, of course) for any 12" *guitar* speaker pulled from, say, Peavey/Crate/Fender/Laney/Hartke/whatever .
Usual prices go around $20/25 and in fact are quite good sounding.

Being a low power amp, an old Jensen pulled from an organ would be enough and sound is killer, better than modern ones.

It will be hard to find a 4 ohms speaker, but an 8 ohms one will work perfectly fine there, and I much prefer an 8 ohm guitar speaker there than any 4 ohm Car Audio monstrosity.

Avoid Hi Fi woofers , specially those with foam edge like the plague.