Stereo valve amp not working.

[Don_Zalmrol]

This just came to me.

When I use my amplifier, I always listen with it to the television or my computer. And I play the sound trough a headset which is connected to the amplifier with a jack-input with decoupling (or how you say it in English) function to turn the speakers off and activate the headset.

Could this usage make my valve's wear faster?
And what is the average life span of a valve?

[Station X]

If valve #2 does not overheat in other sockets, this suggests a problem with the bias voltage on socket #2. Check the voltage on pin 5 of all sockets.

Are the other valves OK in socket #2?

[Don_Zalmrol]

Yes, they are "ok". They just light up a bit brighter, so the valve in that socket gets more power.

I will measure it.

[Don_Zalmrol]

438V and on the other valve socket 1 439V

[Station X]

If you have 439V on pin 5, which is the control grid, you have serious problems. The voltage here should be negative.

[Don_Zalmrol]

Ow, sorry wrong pin.

On every valve socket, pin 5 has a stable -38VDC

[Station X]

And something I am curious about is why isn't valve #2 not overheating on the other valve sockets?

I am curious about that too. Are you saying that ONE PARTICULAR valve, which we'll call #2, only overheats in one socket, which we'll call socket #2, and is OK in all the other sockets?

If that is the case I'd say that valve #2 is very sensitive to variations in bias voltage, which must be lower on valve socket #2.

EDIT. We crossed in the post. If what I say above is true it must be due to something over than bias voltage.

[Don_Zalmrol]

So to recap

pin voltages:

3# 433 VDC
4# 433 VDC
5# -36 VDC (on socket #1, 3, 4 -37 VDC
8# 0V (the same on socket #1, 3, 4)

[Station X]

438V and on the other valve socket 1 439V

I'm curious about this too, because in post #14 you quote voltages in the 465V region.

It would be useful to have a full set of readings for all the output valves.

[Don_Zalmrol]

yes, only that valve (valve #2) is overheating, and yes only in valve socket #2.
And like I said earlier, if you put another valve in socket 2 it works perfectly (not tested with sound) but it "shines" a little brighter than the other valves…

So what could the error be?
The valve is too sensitive?

EDIT:
Do I need to measure also the little valve's or only the E34L's?

[Station X]

Only the E34Ls.

[Don_Zalmrol]

Allright, I'm going to measure them.

Might the different voltages from before be because the pre-amp valves were not installed? If so, sorry. I'm a novice on valve amps.

[Station X]

You need to have all valves installed when taking readings. The reason for this is that more valves consume more current, which causes the High Tension (HT) voltage to fall. Similarly if you have fewer valves installed the HT voltage will rise.

[Don_Zalmrol]

Note: The amplifier isn't connected to an audio source and their are no speakers connected to it.

socket 1 | pin voltages:

3# 434 VDC
4# 435 VDC
5# -38 VDC
8# 0V


socket 2 | pin voltages:

3# 433 VDC
4# 434 VDC
5# -36 VDC
8# 0V


socket 3 | pin voltages:

3# 433 VDC
4# 434 VDC
5# -37 VDC
8# 0V


socket 4 | pin voltages:

3# 434 VDC
4# 435 VDC
5# -37 VDC
8# 0V

And again on every pin 8 the voltage is 0

[Station X]

Very good.

Please connect some speakers. It's kinder to the output transformers.

You will notice that the bias voltage on pin #5 of socket #2 is lower than that on the other valveholders. This will cause any valve plugged into that socket to consume more current than it would if plugged into say socket #1.

Do you have instructions for setting the bias?

[mark pirate]

Don't run the amp with no speakers attached, you will damage the output transformers!

Mark

[Don_Zalmrol]

Thx, I will go and get my speakers. I didn't know it could harm the output transformers.
I don't know how to set the bias, but guessing it would have something to do with "fine tuning" the variable resistors…

Do I need to re-test every voltage with speakers or not?

[Station X]

I have to sign off now. You could try adjusting the bias on #2 valveholder. Monitor pin 5 and adjust the bias control so the voltage increases ie goes more negative. This should make the valve consume less current and stop the anode glowing so much.

If this amp is sold as a kit the instructions should be available somewhere and will describe how to set the bias. It may be simply set to give a specified grid voltage, or the bias may have to be adjusted to give a specified anode current. To measure anode current you'd need to connect an ammeter in series with the anode circuit.

No need to recheck the voltages with speakers connected, as we've been measuring voltages with no input signal.

[Don_Zalmrol]

Ok, Thank you for you're help!

I will make the bias equal to the -38V like valve 1, does valves 3 & 4 also need to be -38V or may they stay as is?

The book doesn't mention the bias, only showing pictures as a circuit guide. It's a kit from China…

What would the anode current be (an educated guess)?

Oh, and if the bias is adjusted.
Do I need to replace valve #2?
It looks a bit burned from the overheating…

Cheers!

[glowinganode]

Originally Posted by Don_Zalmrol

Note: The amplifier isn't connected to an audio source and their are no speakers connected to it.

socket 1 | pin voltages:

3# 434 VDC
4# 435 VDC
5# -38 VDC
8# 0V


socket 2 | pin voltages:

3# 433 VDC
4# 434 VDC
5# -36 VDC
8# 0V


socket 3 | pin voltages:

3# 433 VDC
4# 434 VDC
5# -37 VDC
8# 0V


socket 4 | pin voltages:

3# 434 VDC
4# 435 VDC
5# -37 VDC
8# 0V

And again on every pin 8 the voltage is 0

Hi, these voltages seem quite normal so it would be worth looking at the valves themselves.
An open circuit electrode (g1) or a gassy tube could cause the fault you describe, whilst still giving "normal" meter readings.
You need to find a way of measuring the current through each valve, this is usually done by measuring the voltage across the cathode resistor and applying ohm's law. It would be worth adding these if not already fitted, 10 ohms would be a suitable value.
I would guess the standing cathode current should be around 60 - 65 ma's per valve
Does the fault occur immediately or gradually over time maybe one hour?
Does the faulty valve glow purple on the inside?
What colour is the getter flash at the top of the valve? It should be shiny, brown or dull grey is a bad sign.
Has the amplifier been dropped at any time?
Thanks,
Rob.