Damn it - Black Pearl Issues!! Can anyone help?

[DrumAl]

Right, I'm not sure how many of you followed this thread : http://forum.musicradar.com/showthre...-Of-A-Discount! but following my successful first outing I've now got an issue (nightmare!).

I was playing it today on my studio volume (15 watt/ 2 EL84 - pentode mode) and the initial volume seemed quiet for a minute or so and then it seemed to hit full volume when I switched my comp on. Once I turned that off, the volume was normal then too. I continued playing for 5 minutes and all was well, then I lost volume again before it came back and then faded. Before that I noticed that the rectifier valve was rattling again (goddamn it!!) also.

Any suggestions on what might be at fault, I was hoping just the rectifier maybe but also thought it might be duff power valves. Any help would be greatly appreciated!

Thanks guys.

Al

[Cirrusband]

It's hard to say without trying some things. Do you have any GZ34s/ matched quads of EL84s lying round? If so it'd definitely be worth swapping them out and seeing if that resolves things.

If it'd help I could lend you the stock tubes that came in mine to try out. They seemed to work fine, though one of the EL84s looked like it was on the cusp of starting to redplate after several hours of playing.

[Dave_Mc]

that sucks As i said in the other thread, hopefully it's the valves. I'll just lurk around here to see what one of the resident amp gurus says it might be. FWIW, since you mentioned the rectifier valve, on both of mine the rectifier valve wasn't in that tightly, but it wasn't enough to stop the second one from working, either.

[DrumAl]

It's hard to say without trying some things. Do you have any GZ34s/ matched quads of EL84s lying round? If so it'd definitely be worth swapping them out and seeing if that resolves things.

If it'd help I could lend you the stock tubes that came in mine to try out. They seemed to work fine, though one of the EL84s looked like it was on the cusp of starting to redplate after several hours of playing.

Cheers for the offer dude, I've got some pre-amp valves I can test with and 2 EL84's I can swap in as well. I've just got a sneaking suspicion its the rectifier based on the sound I had, I've heard failing EL84's before and that was a crackling/static sounding noise and it didn't sound like that. Unfortunately I have no spare GZ34 lying around or a solid state spare (which I shall be ordering asap!! anyone got any recommendations for a good one?), but I've just ordered a NOS Mullard one which hopefully will be reliable for a while to come.

Once thats arrived I'll swap it in and see what happens, hopefully that will be problem solved!

[DrumAl]

that sucks As i said in the other thread, hopefully it's the valves. I'll just lurk around here to see what one of the resident amp gurus says it might be. FWIW, since you mentioned the rectifier valve, on both of mine the rectifier valve wasn't in that tightly, but it wasn't enough to stop the second one from working, either.

Cheers Dave, tis a nightmare but hopefully nothing terminal. I emailed GAK last week to check the cover on the amp before I decided to keep it and they said they would honour the warranty. Once I've isolated the problem I will email them to get some replacements or money back or whatever!

I shall keep you updated of course and fingers crossed a few of the amp guru's will tune in soon to confirm my suspicions!!

:-)

[ICBM]

It's definitely worth checking for loose valves before anything.

Did the volume changes happen instantly, or fade in and out? If fading, over one or two seconds, or a longer time?

Instant: signal path problem (not rectifier).

1-2 seconds: HT problem (this can include the rectifier).

5-10 seconds: filament circuit problem (could possibly include the rectifier, although a rectifier filament problem would most likely kill the sound entirely since the two filaments have common pin connections).

It's worth having a spare rectifier even if you get a Mullard - they're high quality but they can still fail. A solid-state plug-in is a good idea.

[Dave_Mc]

Cheers Dave, tis a nightmare but hopefully nothing terminal. I emailed GAK last week to check the cover on the amp before I decided to keep it and they said they would honour the warranty. Once I've isolated the problem I will email them to get some replacements or money back or whatever!

I shall keep you updated of course and fingers crossed a few of the amp guru's will tune in soon to confirm my suspicions!!

:-)

yeah i'll be interested to see what's wrong. Just in case. Good luck

[DrumAl]

It's definitely worth checking for loose valves before anything.

Did the volume changes happen instantly, or fade in and out? If fading, over one or two seconds, or a longer time?

Instant: signal path problem (not rectifier).

1-2 seconds: HT problem (this can include the rectifier).

5-10 seconds: filament circuit problem (could possibly include the rectifier, although a rectifier filament problem would most likely kill the sound entirely since the two filaments have common pin connections).

It's worth having a spare rectifier even if you get a Mullard - they're high quality but they can still fail. A solid-state plug-in is a good idea.

Hi ICBM,

Thanks for posting, I was hoping some of you tech savvy folk would help out!!

The volume changes weren't like a sudden switch more a quick change (if that makes sense!) so I would say the 1-2 second HT problem would be the most appropriate choice of the 3. All the valves are well held in as I'm sure the other BP owners will tell you, very overbuilt holders! I took out the rectifier and give it a small tap/little shake and there's a definite rattle coming from it (I'm not sure if that's a normal feature of a GZ34 but I'm thinking its not). So maybe that's the root cause?

Can I ask if by HT you mean high tension?

I have ordered a solid state version as well so I can isolate any problems elsewhere if issues still arise.

Cheers mate.

[ICBM]

Yes, HT = high tension (high voltage) - fed by the rectifier to the rest of the circuit. A valve rectifier usually has two separate halves which operate on the two sides of the waveform, so if one side stops working the power supply voltage will fall and the volume will go down, and you will also hear more hum (I forgot to ask that) - but it won't go silent.

A lot of modern rectifier valves are very poor quality, so I would certainly start there - a spare is always worth having anyway, and if it doesn't fix it it was still worthwhile getting one. Unfortunately if it doesn't prove to be the rectifier it's a trip to the tech, since the most likely cause is then some other internal problem in the HT circuit.

[DrumAl]

Yes, HT = high tension (high voltage) - fed by the rectifier to the rest of the circuit. A valve rectifier usually has two separate halves which operate on the two sides of the waveform, so if one side stops working the power supply voltage will fall and the volume will go down, and you will also hear more hum (I forgot to ask that) - but it won't go silent.

A lot of modern rectifier valves are very poor quality, so I would certainly start there - a spare is always worth having anyway, and if it doesn't fix it it was still worthwhile getting one. Unfortunately if it doesn't prove to be the rectifier it's a trip to the tech, since the most likely cause is then some other internal problem in the HT circuit.

Cheers mate, thanks for that. There was a small increase in hum too, so fingers crossed that's the issue.

Hoping that I don't have to visit the tech!

If I can just ask you as well, the instructions for the amp say that as its cathode biased I can replace the EL84's without re-biasing. If that's the case can I use any mismatched EL84's in the power section or should I used matched pairs or quads?

Cheers ICBM!