Mystery amplifier

[Kokotoni Will]

I went to the auction house this morning, and they agreed to ask the previous owner if it'd be ok if I got in touch.

Earlier, I was looking at the auction catalogue from that day, and one particular lot looks like it might have had the missing control panel. Techman, does anything from this lot resemble what you'd expect?

https://www.warwickauctions.co.uk/catalogue/lot/020409cb3b75...eral-antiques-collectibles-lot-609/

In other news, I'm starting to attempt to make a circuit diagram, but am unable to identify two of the valves in the amp, namely the ones 2nd and 7th from left. I've attached a photo. I'm guessing it's a tetrode because of the two grids.

[Richardgr]

Regarding the different connections on the OPT secondaries, it could have been set that way for some sort of mono operation with a woofer and high range speaker.

[Diabolical Artificer]

Looks like an ECC83 dual triode type valve maybe a E2164. The circuit may be based on the Mullard 5-10, what are the other amp valves?

Andy.

[Kokotoni Will]

Originally Posted by Diabolical Artificer

Looks like an ECC83 dual triode type valve maybe a E2164. The circuit may be based on the Mullard 5-10, what are the other amp valves?

Andy.

CV 4006 in 1st and 8th position, and CV 2179 in pos. 3-6.

[Welsh Anorak]

I don't think the other lot has what you need.
The chrome coloured amplifier is one I vaguely recognise as a kit from the Seventies and nowhere near the quality of your items.
You never know what's in the boxes, but it looks unlikely.

[Techman]

It'll be brilliant if you can get in touch with the previous owner - fingers crossed!

I can't see anything in those pictures that relates to your amplifier. I also recognise that kit built amplifier and I think I've got an example of it somewhere, but can't remember what the name is.

Regarding the Jones plug, I wouldn't like to say whether it would fit after removing the round pin, it looks to be the same otherwise. Only around half of the connections are used, with several being linked, so you could possibly fit a different type with less connections. I would wait and see what happens as regards possibly contacting the previous owner.

[Diabolical Artificer]

I'm getting a strong vibe that the designer/builder of your amp worked in some military tech type job. The transformers scream Navy, the Parmeko Neptune series tfmrs were used in naval applications so maybe he was an Artificer.

Add to that all the valves have CV numbers IE mil spec valves, enforces that impression. He looks like he had access to a stock of valves from the stores.

I can't place valves in the circuit by your position numbers but the Mullard 5-10 which was extensively built by DIYers used a pentode as V1 IE gain stage so that may be your CV4006 then a dual triode, IE your "641" valve as the phase splitter or V2 then a pair of OP pentodes your CV2179 possibly. See here - https://www.r-type.org/articles/art-003e.htm - see if any of the component values & circuitry match.

Lastly as others have noted your amp is well built by an expert with quality components. Whilst it may be based on the 5-10 (Brimar SP25 rings a bell) he's built a regulated power supply. Re the latter's connection plug etc, I advise using better plus & sockets, separating the AC heater wiring from the HV DC supplies.

Andy.

[jamesperrett]

Originally Posted by Welsh Anorak

The chrome coloured amplifier is one I vaguely recognise as a kit from the Seventies and nowhere near the quality of your items.

I think that's the Powertran version of the classic PW Texan amplifier.

[Radio Wrangler]

Could the regulated power supply have been for a preamp unit rarther than for the power amps?

David

[knobtwiddler]

It's not the easiest course of action I admit, but I've had results with a similar multi-pin connector assembly, where a friend went through the Mouser catalogue to find the male pins individually - and then 3D printed a housing for them. Obviously, you also need to understand the function of the relevant pins before you do this, as some may need individual screening or higher current wire. If you can find the pins, there are websites where you can engage a freelancer (fiverr.com is the obvious one) to do the CAD for you. JLC (in China - but there are local firms in the UK who will likely charge a lot more) will 3D print it for you.

This may seem like a lot of work...which it is.

[CambridgeWorks]

To maybe jog someone's memory in case they might have similar,
I think that Pye Telecom used very similar length connectors on the 1950s early 60s boot mount PTC**** series 2 way mobile radios.
Whereas the later Vanguard and Cambridge models used the shorter length type.
Whether or not a locating pin was there, I don't know.
Rob

[Radio Wrangler]

It's very likely that the Jones plug on the power amp chassis is purely for power supply. The BNC connectors are screened and will be for the signal. As far as the jones connector on the power supply goes, I can't see any reason why signals will be routed to this unit. So the cable harness is unlikely to have to contain any screened conductors. The preamp/control box however done is likely to have BNC output connectors to allow independent cables straight to the power amp.

It looks like the genders of the Jones connectors are such that if either end is disconnected, there are no live pins exposed, which is how they should be used.

David

[knobtwiddler]

It's very likely that the Jones plug on the power amp chassis is purely for power supply

A quick zoom on the photo suggests that you are likely correct, with only 7 of the conductors being used from what I can see (unused pins are wired in parallel - suggesting it's the work of someone who's put thought into field reliability). It should be easy work for a decent technician to find an equivalent replacement in light of this. The question is, can it be kept as neat as it is now? That will be a tall order, as the amp is beautifully crafted. The person who made it had training.

[Techman]

It's just heaters and HT on that Jones socket. I was in Lincoln today and was in Birketts and asked what 24 pin Jones plugs they had. We looked at a few, but none of them were of the type you need. There were some with more pins and some with less and most had that single round locating pin, but it was worth a try.

There's still a reasonable chance that the OP may be put in contact with the person that put the amplifier into the auction sale and it may yet yield the missing bits. It could have come from a house clearance or it could be relatives of the original builder or even the builder himself, depending on the circumstances. We'll have to wait and see what happens.

I have to admit that at the start of this thread I wasn't at all confident that the OP would be capable of being able to do anything with this amplifier and its power unit, but now I'm a lot more confident that he can do something with it, even if it means obtaining and fitting a different type of plug and socket arrangement, but it'll require a lot of careful work to do it.

[Radio Wrangler]

t might be worth starting to trace out just what the extra pins on the large Jones socket on the power supplt are connected to.

I'm suspecting that the missing cable was more of a harness than a point-to-point link, carrying lower HT voltages to a preamp and maybe a tuner.

It's information that's going to be needed anyway, so some circuit tracing can go on while responses relating to the cable are awaited.

If nothing turns up, then finding an alternate style of connector for both PSU and power amp will be the only viable way forwards, unless someone comes up with the mating versions of the Jones connectors.

David

[Kokotoni Will]

Thanks for having a look for the Jones plug, Techman. I didn't get a reply from the auction house, so I went there again this morning. I was told that the amp had been sold via an agency, as part of a deceased estate, and so they could not contact the original owners. A shame, but never mind. I think it may be possible to drill a hole to accommodate the guide pin that the 24 pin connectors on eBay seem to have. Alternatively, I may be able to build a cable using two separate Jones plugs, one for the heater windings and one for HT and HT earth.

The circuit diagram is coming along. As for the Jones plug, brown looks like the heater wires for the 12E1 and CV38 valves, green is mains earth, white is HT earth (from the voltage pot, left lug, via an 18k resistor) and red is HT (from voltage pot, right lug, via a 0.25uf 500v cap).

The two small valves circled in yellow are proving hard to identify. They are marked something like R78, R73 or R7B, and have 7 pins. I've attached a photo of one of them.

I've found that the 47k resistor circled in red, that goes between pin 1 of the upper valve circled in yellow and the fuse in the top right, measures 13M ohms, so it must have failed.

[turretslug]

The valve pictured could be an 85A2, a popular voltage reference in many regulator circuits, the dark-finish glass is a characteristic of these types.

[seymour32]

Hi, is this the correct plug you need?
https://www.ebay.co.uk/itm/276883338659

[Kokotoni Will]

Here's the power supply circuit diagram.

[Kokotoni Will]

Originally Posted by turretslug

The valve pictured could be an 85A2, a popular voltage reference in many regulator circuits, the dark-finish glass is a characteristic of these types.

Yes, that matches the pinouts. Thanks.

Originally Posted by seymour32

Hi, is this the correct plug you need?
https://www.ebay.co.uk/itm/276883338659

That's the one. I've ended up buying another like it, without the metal enclosure, which I'll attempt to make.