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

[Capgun]

Primo, Cade? You guys are great. I thank you for the help. I'd love to learn more, about electronic solid state, and Tube amp and receiver repair. You guys point the way, and I'll read up on it. I have the Variac now of course, and a MultiMeter. I bought the MultiMeter years ago, only to test voltage, in my Li-Poly batteries, before and after charging and balancing. For all the rest of you, thanks to you also.

P.S. Cade? My audio buddy Jim had first dibs on it, and since it didn't involve shipping, and he's a friend, he got it. In the same deal, I got a Monarch FM-100 Tube Receiver. I didn't test it. But you are welcome to it for free, except shipping. let me know.

 

[triode17]

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.

True, you will get some voltage on the output Tx's. But I am not happy until it works. That's why I always set a device that I think is OK up to act like an amp. right away - input signal, load . Although the signal looks crappy at low voltage, if it will produce some kind of signal, that tells me it's basically behaving.

 

[primosounds]

True, you will get some voltage on the output Tx's. But I am not happy until it works. That's why I always set a device that I think is OK up to act like an amp. right away - input signal, load . Although the signal looks crappy at low voltage, if it will produce some kind of signal, that tells me it's basically behaving.

The low voltage check is just an initial check on first power up. It would be no point going further if either the power or output trans were defective. At the least you will be on alert to pay closer attention to the problem or potential problem.
From this point you obviously need to go further with increased voltages. And at around 50% of the variac, one would install speakers and with them installed you should start to have some audio coming through. At 75% of wall voltage, there should be sufficient audio signal to drive the amp to produce sound through the speakers.

 

[triode17]

The low voltage check is just an initial check on first power up. It would be no point going further if either the power or output trans were defective. At the least you will be on alert to pay closer attention to the problem or potential problem.
From this point you obviously need to go further with increased voltages. And at around 50% of the variac, one would install speakers and with them installed you should start to have some audio coming through. At 75% of wall voltage, there should be sufficient audio signal to drive the amp to produce sound through the speakers.

Another thing I don't do is to hook them to speakers until it has passed my bench test - Run at 1 W for 30 mins, then 1/3 power for 30 mins. Only then will I connect it to speakers.

 

[primosounds]

Another thing I don't do is to hook them to speakers until it has passed my bench test - Run at 1 W for 30 mins, then 1/3 power for 30 mins. Only then will I connect it to speakers.

This is not an acceptable procedure for tube amps. Tube amps need a load or they can go into a self destructive oscillation. The load doesnt need to be a speaker, it can be a 50w 8 ohm resistor or something similar. I prefer to use a cheap speaker so i can hear what is going on with the amp.

 

[primosounds]

Too fast on old amps you need to give the filters caps to reform the isolation should run the AC up to 25 volts and let It have time like 12 hours then 50 same time 75 then 117 this is best done with tubes pulled check all the tubes before there used agin and allwise have it connected to a load , even a short it better than open !
B

the procedure i am describing is not to reform caps. I seldom, erm, actually never, reuse electrolytic caps. It is just too much of a gamble to reuse them.

 

[Groovin]

I see the term "B+" a lot when reading these things like B+ on the plates as mentioned here.

How do you test for that on a tube guitar amp? Obviously starts with a DMM i assume. What setting on the dmm, is it DCv? I have a set of bias sockets, will i use those?

 

[triode17]

This is not an acceptable procedure for tube amps. Tube amps need a load or they can go into a self destructive oscillation. The load doesnt need to be a speaker, it can be a 50w 8 ohm resistor or something similar. I prefer to use a cheap speaker so i can hear what is going on with the amp.

Well of course I use a load. Non-inductive, 8 Ohms.

 

[cademan]

I see the term "B+" a lot when reading these things like B+ on the plates as mentioned here.

How do you test for that on a tube guitar amp? Obviously starts with a DMM i assume. What setting on the dmm, is it DCv? I have a set of bias sockets, will i use those?

B+ was a term when battery powered tube radios or farm radios were once the norm before they were built to run on the up and coming new power system or the AC main lines. The tubes in these battery powered radios needed 3 different power supplies to operate. Filament, bias and plate voltages. The filament voltage was known as the A power supply. The bias voltage was the C power supply, and the plates were the B power supply. The old farm radios of the 20's & 30's usually (at that time) used low filament voltage tubes such as as 1U4 type of tube which only needed a 1 volt source for the filaments. Think of 1 1/2 volt batteries doing this. The bias required another battery and the plates required even another battery (usually a 90 volt battery) for what we use the term now as the B+ power source.

When radios began being manufactured with built in power supplies to run off of the main lines, they were using transformers and rectifier tubes to recreate all of the battery voltages without using batteries.

Now take a typical tube radio or amplifier today which has a built in power transformer. This transformer takes the 120 volts mains and transforms it into basically 3 different working voltages.

1) 5 volts
2) 6.3 volts
3) high voltage (usually in the hundreds of volts).

Most rectifier tubes are 5 volt and this is for the filament. Solid state rectifiers do not need a 5 volt winding from the power transformer.

6.3 volts is for the other tubes filaments only.

The winding that supplies the high voltage to the plates is what's known as the B+ voltage.This voltage gets rectified by the rectifier tube and now the high voltage (let's say 300 volts) is now changed into 300 volts DC or the B+ voltage. This 300 volts DC is for the plates of all of the tubes. They need high DC voltage to operate. No tube can operate on AC except for the filaments only
Read this:

https://en.wikipedia.org/wiki/Vacuum_tube

 

[cademan]

This might help. This is a schematic representation of the power supply to a tube amplifier.

 

[Capgun]

Hi again Cade. Next batch of old vintage radios, amps, and such, I'll hit you up, and give you something for the help you gave me. It should be tomorrow, that I get a new batch.