HEEEELLLLPPPP!! Croft mono problem

[Bigbird]

Hi all , ive got an issue with my right Croft 7r monoblock .

Ive just got out the shower to realise that no sound was coming through the right speaker but it was fine earlier .
After playing around with the cables ,with no results , i opened up the mono to find that the input valve(12bh7) was not glowing but the others were. (Pictured)

I thought one of my newest valves may have blown so i switched back in my old spares but still there is no glowing from them either and still no sound in right chanel .

Im wondering wether something has blown? Seems odd as they were only serviced and upgraded about 9-10 months ago.

I have noticed occasionally and intermittently (maybe 5-6 times) since i bought them a few months back, that this mono doesnt always fire up properly . It has soft start to allow the valves to warm up ,then the power light on the front panel turns from red to green after a few minutes to signal its ready. Sometimes the light would stay red and not click to green after long periods and i would have to switch it off and back on before it would play ball.

Im wondering if its an issue thats reared its head or im just unlucky and something has blown?? I cant see anything with any damage inside though and they have not been moved once since i set them up apart from opening the top up to carefully remove the input valves for newer ones.

Any help or knowledge would be great. Hopefully i dont have to send them back to Glenn in the UK [emoji1695]

Cheers

Karlhttps://uploads.tapatalk-cdn.com/20190820/dc60d168016161fe66f582c3428bb16f.jpg


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[AJSki2fly]

Hi Karl

I had a similar problem with one of my mono blocks (not Croft) this was caused by a failed capacitor on the heater circuit the valve. I think it will be a matter of getting it checked over and fixed, especially if it has been problematic from day one. It should not be too costly to fix just a pain sending it back.

[Bigbird]

Hi Karl

I had a similar problem with one of my mono blocks (not Croft) this was caused by a failed capacitor on the heater circuit the valve. I think it will be a matter of getting it checked over and fixed, especially if it has been problematic from day one. It should not be too costly to fix just a pain sending it back.


Thanks for the reply mate. I had a feeling it would be something like that. I do know a guy here in Oz that services Audio research and Macintosh amps so im thinking he may be able to work it out, but it would obviously be best for Glenn to do it . The shipping alone would be about 80 quid each way , plus the repair costs, so it starts getting expensive which is making me consider the guy i know here.


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[eksiil]

I had a similar issue with the warm-up circuit. contacted Glenn about repairs who said it was OK having it done locally (Estonia in my case, the other end of Europe). which is what I did. however, my 12bh7's were not playing up. I've gone through a fair number of fuses over the years, but it's been worth it.

good luck with getting your amp sorted.

[Opti-cal]

If sending to Glenn maybe best to wait until the Ashes are (nearly) over ey cobber . . .

[Audio Al]

Why not send it back to Glen Croft ? :scratch::scratch:

[Firebottle]

Hi Karl, I don't think it will be a big job, or complicated to fix. Normally with Croft amps, certainly preamps, Glenn uses a 12V regulator and wires two 6V heaters in series.

To confirm look for a regulator chip marked 7812 bolted to the bottom of the case at the power supply end.
This may not be the case with the 7r, it may have 6V AC heaters direct from mains transformer.

Have you tried the valve from the other mono to check it's not the valve?
Have a careful look at the wiring on the valve base to see if there is a dry joint.

Post a pic on here if that helps.

[Macca]

Why not send it back to Glen Croft ? :scratch::scratch:

From Australia?

Not a complex fix so I'd have thought any competent EE would have no issues with sorting it, shipping it all the way back here to be fixed would be nuts.

[Bigbird]

Hi guys thanks for the replies. As already expressed ive moved to Oz so sending it back is the last thing i wanna do really. Ive already emailed Glenn a few times over the past few months to talk about possible updates and valves but never had a reply so maybe i have the wrong email (glenn@croftacoustics.co.uk)???
Alan ive tried a couple of valves and theyre all the same result. Heres a few pics of the inside. No evidence of solder issues that i can see. Maybe one of you can point me to the area i need to be. https://uploads.tapatalk-cdn.com/20190820/76bb5ceae2ab4d67da8e539ea351e39b.jpghttps://uploads.tapatalk-cdn.com/20190820/47fcf5255f10a101921a3d43937f1579.jpghttps://uploads.tapatalk-cdn.com/20190820/aeaa95b95fe94871e402a30aeeb8f05f.jpg


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[Bigbird]

https://uploads.tapatalk-cdn.com/20190820/211a5d170cce8ea6ed8dd64c766511cb.jpg


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[Firebottle]

See if you can follow the wires from pins 4 and 5 on the valve base to where they come from at the power supply end.
The smaller transformer is almost certainly the one providing the heater supply, there should be a low voltage somewhere between 6 and 16V (depending if there is a regulator chip used) on one of the large horizontal capacitors between the two transformers.

If you are not confident about measuring voltages then take it to your local EE, there are high voltages present as well.

[Bigbird]

See if you can follow the wires from pins 4 and 5 on the valve base to where they come from at the power supply end.
The smaller transformer is almost certainly the one providing the heater supply, there should be a low voltage somewhere between 6 and 16V (depending if there is a regulator chip used) on one of the large horizontal capacitors between the two transformers.

If you are not confident about measuring voltages then take it to your local EE, there are high voltages present as well.

Thanks Alan, ive spoken with an EE today who said he can look at it in 3 weeks. Hes the local Audio research and Macintosh service guy so he knows his stuff. He also told me to turn it off and leave it be as there are lethal voltages inside so i think i may leave it to the pro’s on this one. I like my music (and life) to much to be found dead , with an old valve and screwdriver in my hands[emoji23] Was hoping it would be a simple in and out jobby i could solder myself but i dont fancy getting a serious shock or effing up a bloody good amp. Will just have to be patient on this one and maybe Glenn will reply this time with some more insight.

Thanks for taking the time to reply matey

Karl


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[Firebottle]

OK, keep us updated as to what the fault is, for future reference.

[Bigbird]

OK, keep us updated as to what the fault is, for future reference.

Will do buddy. Cheers


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[Bigbird]

Glenn has now been in contact to let me know that he also thinks its the heater supply that feeds the valve and relay board.

Just need to wait for the repair quotes now and work out the most cost effective route to take.




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[Bigbird]

The amp is now back from the dead after a painfully long wait.

The culprit was a 12v regulator that heats the filament.

Right off the bat the sound is in a different stratosphere to the Rega brio that was on standby. Man id almost forgot how bloody good it is,its been so long. Its like having a new amp all over again. Time to nerd out in my chair[emoji1373]


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[Firebottle]

Excellent news Karl :cool:

[Bigbird]

Excellent news Karl :cool:

Thanks for your help Alan


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[Majsterjanek]

Hello Karl, long shot, I've bought these Croft R7's from you and just now found out here they had the problem within previously, thing is I've used them only handful of times before they went to storage waiting for a right equipment i wanted to get that would go with them, and that didn't happen for a long time up until now, i set it all up and switched them both, this is what happened next: after 1 minute one of them clicked on but the other took about 2 minutes to fire up (now it got back to me that when i got them from you they did that too, not concerning really at that time as they worked fine then, today i switched them off for a few hours and tried to switch them on but only one of them is working, i switched off and on few times took a break and switched on again, no success, little frustrated now that i didn't test it properly when they arrived from you but as i said i wanted to run them with a matching equipment that i lacked at that time (was hunting mainly for a matching PRE and more sensitive speakers. Anyway, I'm not expecting anything now from you, little dissapointed here that you did't share this info on your listing that this unit has been repaired previously, could you please let me know what exactly issue was? I've just found by chance this post of yours from before you sold them to me... you say 'The culprit was a 12v regulator that heats the filament." is that correct? can you advice please? Do you think i need to contact Glenn or it's a basic repair that i could do local?
Regards
Martin

[Wakefield Turntables]

Glenn Croft has died.?

[Macca]

They're not complex, any EE should be able to diagnose and fix them.

[Bigbird]

Hi Martin as explained in my private message to you these amps were repaired by the Australian Audio research authorised repair guy and were repaired in 2019… along time before you bought them from me. It was a simple fix of the regulator and these things happen from time to time on analogue equipment so not sure why it would now be relevant?

It definitely doesn’t mean these amps were faulty in any way shape or form when I sold them to you which it sounds like you are suggesting?

They were working flawlessly for a long time before I sold them to you and you’ve now had them 2 or 3 years so lord knows what’s happened in the meantime?

You told me you tested them a few times and they were fine(which they were) and now you’re saying in the private message that you wish you’d tested them properly?

I’m more than happy to help in anyway but suggesting that they may have have an underlying fault from when I sent them over a couple of years ago is not cool.

The amps have a soft start to allow everything to warm up so waiting 1-2 minutes for power up is completely normal

check if all of the valves are secure in their sockets and working ok. They should all be glowing . If not switch them out . They’re all nos valves, I think the rca are from the late 50s so this could be a culprit and simple fix as I think sent you spares. I’m not sure if you have any spare power supply valves though which are the mullards that Glenn used. They’re cheap and easy to obtain if this is the issue

If that doesn’t work then give Alan firebottle a shout as he’s well clued up with crofts. Poor Glenn passed away unfortunately.

Dont worry these things are always a simple fix. That’s one of the reasons why we love analogue equipment.


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[Lawrence001]

Where are you in London Martin I'm not an EE but I've had a lot of experience with various types of amps and could help rule anything obvious out.

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[Stranraer]

Looks like you've got plenty of support here Martin, but if you end up needing a trusted engineer near London I've used James at Deco Audio in Aylesbury (just North of London) when my Croft had an issue.
He's fast, efficient and friendly and prices were fair.