two channel amp. Drive chan lifeless and quiet. What could it be?

Cacofonix

Apparently the valves have been checked on this amp we shall call "the potential bargain"

My first thought wss OT but aparently clean chan is fine. So preamp in an active pre circuit but again I'd have expected both chans to be affected.

Clues?

Drew_TNBD

Almost certainly preamp tube.

ICBM

What amp is it?

Cacofonix

Genz Benz Diablo

ICBM

Cacofonix said:

Genz Benz Diablo

OK. I know nothing about these other than that Fender bought the company and some of the models had reliability problems - don't know if this one was one of them.

No schematics seem to be available, and the only pics I can find are too small to tell anything useful.

If it definitely works fine on the clean channel, it's a preamp fault of some sort. If you have a spare 12AX7, try it in each position in turn and see if any of them fixes it. If you don't have a spare, swap the existing ones around and see if anything changes.

If none of that makes any difference, you need a tech.

Cacofonix

We're a bit ahead of ourselves.  It's up for sale at £150 spares/repair, but I'm undecided, as I don't really need another amp (but you know how it is), and I was wondering if it would be economic to get it and try and repair it.

ICBM

It's almost worth that for the valves plus a few other bits.

Whether it's economically repairable really depends how far you can trust the seller's diagnosis that the clean channel is fine and that the valves have been checked. If it is and it's definitely only a distortion channel problem it shouldn't be too hard or expensive. I've seen worse amps to work on, going by the pics.

Cacofonix

Just noticed it's a 230v amp.

So it may be operating at above spec.  Can the biasing change this (apparently it has bias points) or would I have to essentially accept it will be running over spec (I know this mimics another many threads on the same point).

Cacofonix

Ok I've decided to pass.

I'm not really keen on the sound, and it would just be a purchase to fix and resell, which isn't really my thing.  Anyone wants it it's on Facebook group music gear for sale/wanted yorkshire.

Edit: and thanks for the advice.  It's appreciated, as always.

Headphones

230V is the UK norm...

ICBM

Headphones said:

230V is the UK norm…

Only if you believe the Euro-fudge.

Headphones

ICBM said:

Headphones said:

230V is the UK norm…

Only if you believe the Euro-fudge.

What twaddle.

Am I really the only Engineer on here?

ICBM

Headphones said:

ICBM said:

Headphones said:

230V is the UK norm…

Only if you believe the Euro-fudge.

What twaddle.

http://www.twothirtyvolts.org.uk/pdfs/site-info/Explanation_230Volts.pdf

Only the definition has changed. We still get 240V, just with different allowed tolerances so it can be described as 230V.

For what it's worth, where I work the voltage is usually over 250V.

Headphones

See, 230V is the norm!

That's exactly what the standards say.

Since that's the official value, that's what recent equipment has written on it, and of course the kit will have beent tested against this (and a broader range of standards).

The fact that some of the country is at different points within the tolerance is immaterial and potentially misleading.

Here in brizzle it's typically within a vew Volts of 230.

ICBM

I would say it's the other way round - calling it 230V is potentially misleading. While it's true that there will be parts of the country which are closer to 230V than 240V, it is still really 240V that just happens to be a bit low. There are plenty of places which are over 240V as well.

Basically it means that the average is still above 230V, so if you have equipment which is designed to run on 230V rather than 240V - and there is some, which specifically has taps for both voltages but comes pre-connected for 230V in the UK - then it will run over-spec for internal voltages which will increase unreliability, even if it doesn't cause outright failure. I know it will have been proof-tested at 253V at least, but that's not the same as being a good idea to run it like that.

impmann

Measured it 2mins ago - 243.6v. Significantly more than 230, IMHO...

As ICBM says, the 230v thing is a fudge. 

p90fool

Headphones;430824" said:

ICBM said:



Headphones said:

230V is the UK norm…Only if you believe the Euro-fudge.





What twaddle.



Am I really the only Engineer on here?

I just measured mine at 242v, how qualified do you have to be?
Most modern Fenders have 230 and 240v taps, which implies to me that they think it matters, I can't imagine them bothering otherwise.

Headphones

You're missing the point chaps.  As can clearly be seen above, Cacofonix at least has been misled by the belief that UK mains is different to 230V, he stopped considering a purchase (at least in part) for this point.

The purpose of defining a Standard (tolerance being a key part) is to make it unambiguous what we're talking about; the Standard for mains in the UK is defined as 230V, with a tolerance, therfore modern kit, for use in the UK, will be designed against that.  If that weren't the case someone would be having a little legal chat with the supplier in question!

Quite what Fender are doing on their amps is not so clear and I doubt has a lot to do with the present standards in the UK - it could be simple ignorance on their part, use of old stock, a desire to appear retro - or even to pander to misinformation - only the Fender designer could answer that.

Cacofonix

Thank you. 

I was in two minds about it anyway as it was a potential bargain, but a fixer and I don't have room for another amp unless either I keep it and get rid of another (and it would have to fit in my own preferred audio spectrum for that to happen, which by all accounts it doesn't) or turn it, and it kind of defeats the point of a two hour round trip and a diagnostic and extra valve just to punt it back out again.

I am inclined to go with the recommendations and experience of the resident Gurus (Gura?), at least on gear that may be more than a couple of years old.  As to the future, I'm not sure. I wouldn't mind looking at a Bad Cat amp at some stage, but I'll cross that particular bridge when the likelihood arises.

Cacofonix

Incidentally, someone who I suspect to be a regular here is negotiating for it now.