Transformer query.

[bikerhifinut]

Hi gentlemen.
Found this in the junk box. I remember buying it from Maplins a few years ago and it went into an experimental psu.
It does buzz a bit but buried in a suitable case It may not be too noisy.
I looked up OEP transformers site and I think it would be ok for another SE EL84 project if I get a transformer for the EL84 heaters, and use the OEP 6.3V @ 1A tap for either the driver valve(s) or an EZ81 heater?
It dont look very big for a 150mA trannie but the feeble 1 amp heater supply would possibly explain its dinky dimensions.

Data sheet below, the one I have differs in that its a 3.15-0-3.15 heater tap. But the part no is the same D29240F without the -1 at the end.

http://www.oep.co.uk/pdf/D29240F-1.pdf

I now need to find a couple of 5k SE O/P transformers.

Although I have a pair of NOS RS "hygrade" O/P transformers, these look very beefy on the laminations and because they have multiple tappings can be used SE at various impedances and also P-P at 8k CT (4k-0-4k).
Thinks maybe a p-p ECL82 design?

Andy.

[John Caswell]

Hi Andy,
The Mullard cct uses 4 - ECL82 plus an ECC83 as the pre stage and an EZ81 rectifier.
I would use this tx as the HT/rectifier supply and a small toroid to supply the ECL82/ECC83 heaters as Mullard specs a 4A secy for a stereo so 2A for the mono version.
OPTXs are 9Ka-a with 20% taps.
If you want the data on this I am sure I can copy and mail it to you.
The RS Hygrade OPTXs I would save for something like a 5-20 as they were very good indeed. I think they were made by one of the then big manufacturers -Partridge, Parmeko, Gilson, Haddon or Woden. Sadly mostly all gone now sigh!!!!!!!!

John

[bikerhifinut]

Thanks John,
Much appreciated and pretty much along my line of thought.

I have access to the Mullard circuits book and I think I may even have the circuit downloaded somewhere.
I think I may be correct in thinking that I can use the 8k CT transformers and it will alter the output impedances slightly. This may not be a problem as the "Hygrade" transformers have output impedance taps for 2, 7, and 15 ohms. Theres also a table giving the turns ratios.
The main issue is that I dont think I can get UL taps out of it so the circuit would have to be adapted for pentode or triode connection.
It's in the first stages of planning for now.

Andy.

[bikerhifinut]

The RS Hygrade OPTXs I would save for something like a 5-20 as they were very good indeed. I think they were made by one of the then big manufacturers -Partridge, Parmeko, Gilson, Haddon or Woden. Sadly mostly all gone now sigh!!!!!!!!

John[/quote]

I ain't sure they are beefy enough for a 5-20.
Rated at 60mA and no UL taps. They certainly look well made but not for a higher powered amplifier. Maybe a Pair of 6V6 in push pull but thats probably pushing it. I assume I could put 60mA per valve through it in P-P mode as the total current through the wiring would still be only 60mA, or is my maths suspect?
They were initially bought for the 3-3 project but I thought they looked able to handle a bit more than 3 watts. And they are unused in original boxes. I thought they were a bit expensive when I bought them at Tonbridge, but new stuff isnt any cheaper and I am told that the older transformers were much better wound etc as a general rule.

I have some hardware to start a 5-20 project that Richard supplied me with, thats coming closer as I gain experience of scratch builds.

Andy.

[John Caswell]

Hi Andy,
Ahhh it is that hygrade type,
Sorry they had several Txs in the Hygrade range back then and the pair I have are the big multi tapped type so I naturally assumed yours were the same. Serve me right for being a smart ass.
I reckon you could just use them in the Mullard cct as pentodes without changing anything initially just to see how they go.

John

[bikerhifinut]

Theres always the Kecl82 WAD circuit which I have in the files.
I'd need a different mains Transformer though as it runs a lower HT than my 240V job would supply.

Also the Mullard Circuit is too sensitive at 100mV, around 400 to 500 mV would be about ideal for me. Maybe could tweak it with say an ECC82 and a fiddle with the feedback circuit?

All to think about.

Andy.

[bikerhifinut]

I found a new transformer in the toybox, unused. 2 independent secondaries rated at 12V @ 1A each. I think it would be ok to run a pair of EL84/ECL82 in series off each winding and have enough left to heat a small ECC8* type too?
I was going to use it in the next project, but think I may just get a 6V toroid for heater duties.
Havent decided on which ECL82 circuit to use, I also wondered about an ECL86 circuit, shame PCL86 heaters need 14V as they are a lot cheaper.
Did they make a similar version of the ECL82? (PCL82?) I know theres a UCL82 but that needs quite a high heater voltage i think.

Andy.

[John Caswell]

Hi Andy,
Yes you could certainly run an EL84 and ECL82 heater in series but you would need to fit a small R across the EL84 heater to take up the excess 20 mA of current difference between the two. Then the ECC** would go straight across the 12V, with the heaters wired in series ie pin 4 and 5 only used.
Don't use ECL86 too damned expensive and rare now. PCL86 requires 13 odd volts
Yes PCL82 was made, don't know about availability but would think plentiful and cheap (TV valve) but as the 6V version takes 0.78A then the 300mA version will require 6.3 X 0.78/.3 = 16V. and the UCL82 requires 16 X 3 = 48-50V.

John

[bikerhifinut]

thanks John.

Sorry i was a bit confusing, it was either or a pair of EL84 or a pair of ECL82.
I figure now I can use the 150mA transformer and its heater winding for an EZ81, and the 2 x 12v at 1A for 2 pairs of ECL82 and have enough in reserve for an ECC83 preamp Valve if necessary.

Just need a chassis now.

[bob orbell]

If I was still working I could have one made to your spec.Andy, for nowt, oh well, there is always a down side to retirement. BOB