I bought this beast for 50 bucks, but...

[primosounds]

Thank you Battradio and Cademan. I was wondering what that 3 amp flat head looking plastic screw went to. I am an electronics novice, at best. I've replaced Capacitors on crossovers and I know how to solder. I can do pretty much anything on speakers, but, when it comes to amps and receivers, I have soooooooo much to learn.

Seems like you are a hands on type of a guy. So, with your 50 buck outlay for the amp putting way ahead of the curve you should just budget some money for extra gear for the care and feeding of your tube amp. I would suggest a variac and a DMM, is essential. I use a variac everyday for my tube amp work and troubleshooting. Before doing any of your own troubleshooting and testing be sure to read up on the proper safety procedures around a tube amp.
Tubes will start conducting/working as soon as the heater starts getting hot enough to knock electrons off the cathode. This begins at around 40vac very slowly, and usually by 60vac most of the tubes are conducting. So at this point you can measure voltages around the amp. If you have cheap speakers to hook up to the amp, you should hear clicks when your meter probe touches "energized connections. I start testing unknown equipment from the first power supply cap and then step by step to finally end up at the signal tubes. If you want to be safer, you can buy a solid state plug in for the rectifier tube. Since SSR starts working immediately at 10vac. you will have voltage throughout your amp all at non hazardous levels. While starting at 10vac will not tell you that your amp is in working condition, it will let you know that the power trans is working, and the output trans is also working. This is the 2 major components that need to be checked before doing anything else. If either of these are bad then you need to consider whether doing any other work on the amp is even worthwhile. This is a worst case scenario and especially for PA equipment is rare, since they were designed to operate 24/7/365.

 

[Capgun]

Thank you Primo. I'm kinda walking the high wire without much of a net at the moment. I just fired it up about 10 minutes ago, and I dialed it up to 10 volts, slowly. I'm now at 15 volts, and I'm starting to see the 2 light bulbs at the front of the unit, coming to life. About to go to 20 volts.

 

[Capgun]

30 volts, no smoke, no smell and the lights are getting brighter. Primo some of you're short language things, I don't understand. Sorry, but I need the terms explained a bit more please. Thanks!

 

[Capgun]

Okay. I'm at 50 volts now, and from what I've been reading, is to leave it there for 30 minutes. Then dial it up slowly to 75 volts, and leave it there for another 30 minutes. Lights are much brighter. I have all the knobs turned down.

 

[rshep]

I'm enjoying the serialized presentation. Nice iron on the amp, what output tubes does it use?

 

[Capgun]

This is how dumb I am when it comes to these things. I don't know which ones are which. 6L6G I guess?

I'm up to 60 volts now, and I can see 2 tubes lighting up very slightly.

 

[Fairlane]

The suspense is killing me....

 

[Capgun]

I'm up to 75 volts now. Tubes are all lighting up, except 1. They're all still pretty dim though. Anyone who may be watching this, is the one tube that isn't lighting up, a bad thing? I mean like, can I turn the volts up safely, with a possibly dead tube?

 

[Capgun]

I'm at 90 now. I have to leave it here for 15 mins.

 

[Capgun]

110 Volts achieved! It's really a beautiful unit, all lit up! I'm glad nothing blew up, or that I didn't catch on fire. Lol. So what do you guys think? I have to replace that 1 tube obviously, doesn't look like it's going to be cheap.

 

[drtool]

What kind of sound are you getting. Or are you using a dummy load?

 

[Capgun]

I don't have anything to test it further with. Since it's a PA I don't have a microphone. There's a connection for a Turntable, I don't know why. Only thing I know about these is, they are supposed to make great guitar amplifiers, with a little conversion. I'm always willing to take suggestions from way more knowledgeable people.

 

[cademan]

The phono input is what you want to use. It is the same as an AUX input. Just connect a speaker to the 8Ω connection and use a CD player or phone with the right adapters and plug 'em into the phono input.

Back away as you will be blown away. Use a good speaker which produces plenty of bass, rated for at least 50 watts, and get ready to be amazed. Because tube amps use output transformers, there is no possibility of any bad voltages getting to your speakers and blowing them. Just don't connect anything to the 70 volt tap.

 

[Capgun]

Thanks again Cade! I'm heading out for the night. I'm sure I will need you're help tomorrow as I test it further. G'night everyone, until tomorrow!

 

[cademan]

In your post number 30, you have a couple of pics (022.JPG, 023.JPG) which shows the output tubes red plating. This is not a good sign. A total recap is in your best interest before you decide to fire it up again.

No tube should ever glow along the plates as the one's you have showing are doing. It can be bad tubes but in my experience, it is 98% bad coupling capacitors connected to those tubes via the tube sockets underneath.

 

[Chip Chester]

If you're looking to use it as a microphone-level mixer, those four red caps are probably the places for four microphone transformers. Probably difficult and expensive to find -- although you could adapt most any mic transfor (just expensive, not really difficult to find) by wiring them to an octal plug. (Or wiring directly underneath chassis.) Your phono input should work directly, though.

Chip

 

[Capgun]

Hi Cademan. I think I'm just going to sell it to one of my audio friends who will want to fix it.

 

[cademan]

Ooh, ooh ooh ooh! (with one hand high in the air).

 

[triode17]

Seems like you are a hands on type of a guy. So, with your 50 buck outlay for the amp putting way ahead of the curve you should just budget some money for extra gear for the care and feeding of your tube amp. I would suggest a variac and a DMM, is essential. I use a variac everyday for my tube amp work and troubleshooting. Before doing any of your own troubleshooting and testing be sure to read up on the proper safety procedures around a tube amp.
Tubes will start conducting/working as soon as the heater starts getting hot enough to knock electrons off the cathode. This begins at around 40vac very slowly, and usually by 60vac most of the tubes are conducting. So at this point you can measure voltages around the amp. If you have cheap speakers to hook up to the amp, you should hear clicks when your meter probe touches "energized connections. I start testing unknown equipment from the first power supply cap and then step by step to finally end up at the signal tubes. If you want to be safer, you can buy a solid state plug in for the rectifier tube. Since SSR starts working immediately at 10vac. you will have voltage throughout your amp all at non hazardous levels. While starting at 10vac will not tell you that your amp is in working condition, it will let you know that the power trans is working, and the output trans is also working. This is the 2 major components that need to be checked before doing anything else. If either of these are bad then you need to consider whether doing any other work on the amp is even worthwhile. This is a worst case scenario and especially for PA equipment is rare, since they were designed to operate 24/7/365.

Primo, sidenote- At just 10Vac, how could you check that the output Tx. is working? The heaters won't light that low. I find 60v. min. is required.

 

[primosounds]

Primo, sidenote- At just 10Vac, how could you check that the output Tx. is working? The heaters won't light that low. I find 60v. min. is required.

If you are getting B+ voltage and there is no short from the center tap of the primary of the output trans then there will be B+ on the plate connection of the tube socket. You should get B+ on the plate and G2 or UL connections , for both tubes. If you don't then there maybe a problem with your OPT. In other words, before the B+ voltage goes to the power tubes it needs to go thru the OPT via the CT, then UL tap (if used), then Plate tap.