Identifying a Valve Amp (Haverson 10/14).

[phykell]

Hi,

I've been given an old valve amplifier and was wondering if anyone could identify it:

From what I can tell it has a Mullard EZ80 rectifier with a Plessey 50/50 uF capacitor. The small valves are a Mazda ECC83 and an unknown Mullard (no paint left on it for the model) though it looks pretty new (the far left one). The two output valves are a Mullard EL84 and another "EL84 FD" (no brand name).

I plugged in the amplifier and it certainly does produce music though the controls seem a bit odd: from left to right, #1 doesn't seem to do anything, #2 is the volume, #3 is the bass, #4 is the treble and the on/off switch!

I'm a bit concerned at the transformer as it did start to run a bit hot so, having read a little in this forum, have decided that there must be a dodgy capacitor somewhere.

I was hoping that an identification might help me figure out how to get this thing up and running without the transformer heating up!

Any help/advice much appreciated!

[ms660]

Something based on a 5-10 maybe?

[neon indicator]

How hot? If the wax is dripping out it's too hot.

Hot but not burning your hand may be OK. There are no "waxies" so I'd not automatically assume a capacitor problem. It looks like a 1960s "home brew". No doubt the more expert persons can tie it down more accurately.

The wiper of #1 isn't connected, so it won't do anything. Maybe not finished?

[ms660]

I forgot to add that if the valve with the rubbed out markings has an "open weave screen around the electrodes then it could well be an EF86 if this is the case then the valve line up sounds like 5-10.

Lawrence.

[Alistair D]

This looks very like an amplifier from the Linear stable. These were available in the 60s in kit form or ready built.

Have a look at this site. there are a couple of amps that sort of match your valve line up. The site has some references to Linear repairs. You might be able to find a pic that matches yours.

http://www.chambonino.com/carlsbro/carlwires.html

Al

[neon indicator]

It looks more like another ECC83 though. Looks solid

I'd say the other pot was for a 2nd input. There is a spare hole on case too beside input jack



This has 2 x ECC83 http://www.chambonino.com/carlsbro/l...thcourt15.html
and http://www.chambonino.com/carlsbro/linear-rsc-a11.html

The other 2 with 2 x ECC83 and the one with EF86 are using EL34, not EL84

Both those have EZ81 rather than EZ80. But maybe someone fitted EZ80.

See how many wires from EL84s to Audio transformer.

[mickjjo]

Mullard 5-10 details here:-

http://www.r-type.org/static/5-10.htm

Regards, Mick.

[ms660]

Yes you could be right, just got my magnifying glass on the computer screen! it could be another ECC83, when I first looked at the pics it was the two 47r screen feed resistors that made me think it was something based on a 5-10.
All will be revealed in time, the chassis looks factory made.

[GrimJosef]

I'm pretty sure the input valve is an EF86. Pins 8 (g3) and 3 (k) are wired together, which makes sense, and pin 9 (g1) goes via a resistor to the input jack. Several manufacturers made solid screen EF86s, including Mullard http://www.vintagehofner.co.uk/galle...lves/ef86.html.

Cheers,

GJ

EDIT: Then again, maybe not. Is the black wire that loops from the left hand end of the tagstrip via the input jack to the two left hand pots actually grounded ?

[phykell]

Thanks for all the fast and well-informed replies!

If higher-resolution images or close-ups of anything would help I can do that

The transformer does have some wax on the wiring directly underneath it so I presume it is running too hot plus it has a distinct odour when running. The orange Plessey capacitors have a date on them - Jan 63 - I assume they're the original ones.

I thought the pots were intriguing. If it was a home-made unit, you'd think that the stems wouldn't be so long - I'd assumed it was out of some kind of radiogram or similar.

The input jack seems quite modern compared to the rest of the unit and there's another, unoccupied hold adjacent to it.

Would there be any merit in replacing any capacitors before switching it on again or is it best left as-is?

I must admit, it does have a certain unique quality to it. I've hooked it up to my computer and a JBL Control 1X speaker and it sounded great especially on Rolling Stones, Jimi Hendrix, and other 60s guitar stuff plus Hotel California, etc.

[ms660]

Yes I think so, northern most tagstrip, far left tag, just had another look at that valve with my even bigger magnifying glass! that outer electrode is a lot lighter than the ECC83, I tell you what, we could reverse engineer the pic and post the circuit up tomorrow !? If the tranny is still ok fit an HT fuse.

[ms660]

The top chassis layout looks like a Harverson 10/14, search for Harverson on this excellent site and somewhere you will see a sales adv. plus a diagram.

https://www.vintage-radio.net/forum/...ad.php?t=67586

Cheers

[Herald1360]

I still wouldn't trust the metalpack capacitors to the output valve grids from the phase splitter.

Have you got a multimeter or any other test equipment?

[phykell]

Originally Posted by Herald1360

I still wouldn't trust the metalpack capacitors to the output valve grids from the phase splitter.

Have you got a multimeter or any other test equipment?

OK so I can replace those capacitors just in case?

I've got a cheap (£5) DMM but I have got an old Oscilloscope in the attic that probably still works plus various PSUs, a home-made signal generator (very basic) and quite a lot of components, soldering equipment, so I should be able to have a go at getting this unit running OK - just need some guidance plus I'll need to fabricate a shunt

[phykell]

Some better pictures including close-ups of the unmarked Mullard valve:

I've found what I think should be a decent replacement for the 0.1 uF metalpack capacitors:

http://www.maplin.co.uk/metallised-p...rdercode=RG23A

Are there any tests I can do on the valves to see if they're OK? Are there any other components I should pay special attention to?

[phykell]

And more picture

[Herald1360]

Yes replace them....

A £5 DMM will do nicely- ISTR mine was a BOGOF at the same price! Occasionally I resort to a half decent bench one, but not often. Remember it will probably have only 1 megohm input resistance rather than the 10 megohms of a better one.

Once they're replaced, check the output valve cathode resistor(s) for value then try a short run and measure the voltages across them to see whether their cathode currents are reasonable. Also check the control grid voltages which should be within a few mV of zero.

[neon indicator]

Originally Posted by phykell

I thought the pots were intriguing. If it was a home-made unit, you'd think that the stems wouldn't be so long - I'd assumed it was out of some kind of radiogram or similar.

The input jack seems quite modern compared to the rest of the unit and there's another, unoccupied hold adjacent to it.

They come long like that. Or used to.

I noticed that

[G8HQP Dave]

The first valve looks like a screened pentode, probably EF86. The pot wiring seems incomplete - and four pots? Three I can understand. It looks like a fair-to-middling attempt at a kit.

[ms660]

Yes Dave I agree with you...definatly a kit...unfinished the two input pots are there maybe phono & Mic....I would put money on a Harverson 10/14
(maybe !)