Issue with EL34 amplifier

[Lawrence001]

I bought this cheap as it had a crackle but I think the issue is actually that the rear two power valves are not working. The heaters glow but there is no voltage difference across the bias points and I can actually keep my finger on the top for a few seconds unlike the front ones. I've swapped out all the valves with ones that were working fine in my last amp.

Appreciate it's not a trivial question but is there a likely candidate for the fault?

Unfortunately I can't access the amp for a bit but if there are some things I can check for (while it's powered off) I could get a list for next time.https://uploads.tapatalk-cdn.com/20261026/18d6f138f9dcef12cacd8e3ebfb25704.jpghttps://uploads.tapatalk-cdn.com/20261026/ad880067927f3be65410587a56df69e1.jpg

[User211]

The obvious first stab is although you know the tubes were good in your last amp, does the same thing happen if you swap the fronts with the rears?

Expected answer is yes, TBH. But worth a try.

Do all the receptacles for the pins on the sockets look good?

[Firebottle]

If there is no voltage across the bias points that points to no current flow in the valve.

Check the anode connection to the transformer, the cathode resistor if there is one, then the bias pot and associated components that give the negative bias voltage.

[Lawrence001]

Thanks guys makes sense to start with Justin's simple test (as I tried 2 sets of valves and had the same issue, I assumed they were fine but no harm in ruling out). After that I'll try Alan's but I need to work out where those points are and I'm not comfortable with testing voltage from below when it's switched on. Am I right in thinking you can't test voltage without the valves in in a manual bias amp?

[User211]

Ask Alan via PM if he wants to sort it? He might.

If you want to get a much deeper understanding and you have a shit load of time, do it. And educate yourself enough to do it.

So do whatever you think is right for you, basically.

[Firebottle]

Depending on the circuitry you can test for bias voltage without the valves in.

What make and model is the amp? A circuit search is in order.

[Lawrence001]

Ask Alan via PM if he wants to sort it? He might.

If you want to get a much deeper understanding and you have a shit load of time, do it. And educate yourself enough to do it.

So do whatever you think is right for you, basically.I was thinking about that but it's a long way, I don't drive and I don't have the box. So if I can do anything to at least work out what's wrong with it it will be a start. I think it looks pretty well made inside and it weighs a ton so I think it will sound good eventually.

[User211]

Cool. Some problems are pretty simple TBH especially if a component has blatantly failed.

Others are not.

[Lawrence001]

My idea is to use a multimeter to test continuity and measure components as much as possible in circuit, using this diagram as a rough guide as to what an amp with EL34 power valves and octal drivers/phase splitters/whatever they do should be like. Alan has given me some pointers and I might learn a thing or two.https://uploads.tapatalk-cdn.com/20261028/63d61309b325d9eb550132dea69f5bad.jpg

[Firebottle]

Is that the diagram of the actual amplifier laurence?

[Lawrence001]

No I'm just hoping it's a push pull and the basic topology is similar. If I can find a theoretical basic circuit diagram of a push pull EL34 amp with 4 octal valves it would give me a starting point as to what should generally be connected to what on the various stages.

Sorry I didn't answer your earlier question, it's supposed to be a Separo/Pacific Creek EL34i integrated amplifier but I think there may be variations on that. For example the circuit in one in this link looks pretty nasty compared to mine. I suspect it's the basic Chinese version and not the official distributed import version.

https://www.usaudiomart.com/details/649902943-pacific-creek-saparo-el34-integrated-amplifier/