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| Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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7th Apr 2020, 9:30 am
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#1 |
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Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Mystery amplifier
A curious rig has landed on a mate's bench. A passive control unit, a two valve preamplifier on a separate chassis, a power pack with an EZ91 and a power amplifier with two 807s, a slew of 2N3055s and no obvious power supply components. This is from an estate, obviously home brew and supposedly worked once. Said mate is, not unreasonably, looking for some circuit information, but he and I have neer seen anything like this! Does it ring a bell anywhere?
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7th Apr 2020, 10:09 am
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#2 |
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Dekatron
Join Date: Mar 2008
Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.)
Posts: 3,184
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Re: Mystery amplifier
Hi,
Curious indeed. I'm probably completely wrong, but I would have thought that an EZ91 would be too puny to supply a pair of 807s? Or have I misunderstood and the EZ91 is in the pre-amp? Sorry, the coffee hasn't kicked in yet.  Cheers, Pete.
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"Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..." |
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7th Apr 2020, 10:30 am
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#3 |
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Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: Mystery amplifier
Perhaps there is another unit missing?
I think I'd find the speaker output terminals and trace things out backwards, at least the speaker outputs ought to be reasonably overt and unambiguous. Could the 807s be driving the 2N3055s or are the 2N3055s be constant current sources scattered all over the place. Anything is possible. Don't think you'd need 2N3055 to drive 807s. I'm going to watch this one unfold! David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
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7th Apr 2020, 10:47 am
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#4 | |
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Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Re: Mystery amplifier
Quote:
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7th Apr 2020, 1:18 pm
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#5 |
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Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Mystery amplifier
Could it be a modulator for an AM transmitter?
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
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7th Apr 2020, 2:10 pm
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#6 |
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Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Re: Mystery amplifier
No - it was allegedly used to drive the speakers which came with it...
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7th Apr 2020, 11:15 pm
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#7 |
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Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Mystery amplifier
Could be a false allegation......
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....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
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8th Apr 2020, 7:40 am
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#8 |
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Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,670
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Re: Mystery amplifier
Good point Chris, 1st rule of repair 101, " treat with large dose of salt anything customer tells you".
A few pics would help, not much to go on, the 3055's could be used as regulator's for htr supplies or floating/elevated as part of a pre-amp, 300v g2 regulation, or part of dynamic bias. The EZ91 might be there as part of a slow start circuit , all speculation though. Andy.
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Curiosity hasn't killed this cat...so far. |
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8th Apr 2020, 8:09 am
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#9 |
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Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,878
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Re: Mystery amplifier
I have let my imagination run wild on this one!
 How about the 807's are being used as controlled rectifiers/regulators straight off the mains, the EZ91 just supplying power to the controller electronics. The 3055s are then used as conventional transistor amplifier. If any of this is the case its going to be a live chassis design. Yes I am getting cabin fever  Cheers Mike T
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Invisible airwaves crackle with life or at least they used to  Mike T BVWS member. www.cossor.co.uk |
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8th Apr 2020, 8:52 am
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#10 |
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Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: Mystery amplifier
Passive preamplifiers and then valve buffers and hybrid silicon/thermionic amplifiers starts to seem a bit boutique-y to me. The 807 and the 2N3055 eras didn't overlap, so seeing both in one thing seems unnatural.
Come on, Ted, let's see some pictures! David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
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8th Apr 2020, 9:13 am
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#11 |
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Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Re: Mystery amplifier
I've asked - the beast is miles away and not in my care. Agreed, it's utterly boutiquey, though, if not plain daft...
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8th Apr 2020, 3:47 pm
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#12 |
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Moderator
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,225
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Re: Mystery amplifier
Can your friend supply some pictures?
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8th Apr 2020, 3:59 pm
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#13 |
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Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: Mystery amplifier
Sounds like it ought to be entertaining.
I guess I've got to stop thinking of the reproduction of sound and see a wild amplifier as an art-form in itself. The difficult bit is stopping myself giggling. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
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8th Apr 2020, 5:04 pm
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#14 |
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Moderator
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,225
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Re: Mystery amplifier
It could be that its a transistor amp with a couple of 807's and a EZ91 for decoration.
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