Ideas For EL34 Pentode Push-Pull Amplifier

Cressy Snr · Post by **Cressy Snr** » Tue Dec 17, 2013 7:29 pm

Interesting indeed.

Paul Barker · Post by **Paul Barker** » Tue Dec 17, 2013 9:43 pm

Danger danger danger.
Steve, please don't start building all those examples in that article, in case you self destruct!

Cressy Snr · Post by **Cressy Snr** » Tue Dec 17, 2013 9:50 pm

Paul Barker wrote:Danger danger danger.
Steve, please don't start building all those examples in that article, in case you self destruct!

No danger of that Paul. I no longer have the finances to fund such tomfoolery what with being a happy part - timer and all that

Cressy Snr · Post by **Cressy Snr** » Tue Dec 17, 2013 11:33 pm

9pin loktal sockets arrived this morning.
Four EF50s, two 0C3, two 0D3 and eight Belton octal sockets, are on their way.
Output trafos are now at the Rotherham Parcelforce depot, so will be out for delivery in the morning.
Now I have all the ironwork, I'll be able to get the box bent up, built and painted over the Christmas period.

Cressy Snr · Post by **Cressy Snr** » Wed Dec 18, 2013 5:55 pm

Output transformers have arrived.
They are big buggers for push pull transformers!

Something tells me they are going to rather good.

Hopefully the small signal pentodes, gas regs and octal sockets will be here tomorrow.

IslandPink · Post by **IslandPink** » Wed Dec 18, 2013 6:06 pm

Early Christmas , Steve !

Greg · Post by **Greg** » Wed Dec 18, 2013 7:39 pm

SteveTheShadow wrote:Output transformers have arrived.
They are big buggers for push pull transformers!

I recon what Martin has sent you is not the original WAD 300B O/P Tx's which are fairly small, but rather a pair from the much later monoblock 300B PP amps. If they are as good as my SE versions which was a sister amp at the time, they should be very very good. Andrew tested mine at Owston and declared them very good and flat throughout the frequency range. Looking forward to your findings

Cressy Snr · Post by **Cressy Snr** » Thu Dec 19, 2013 10:14 am

Greg wrote:
SteveTheShadow wrote:Output transformers have arrived.
They are big buggers for push pull transformers!
I recon what Martin has sent you is not the original WAD 300B O/P Tx's which are fairly small, but rather a pair from the much later monoblock 300B PP amps. If they are as good as my SE versions which was a sister amp at the time, they should be very very good. Andrew tested mine at Owston and declared them very good and flat throughout the frequency range. Looking forward to your findings

Intriguing.

I've had a look on Google images, which led to this thread on the WD forum.

http://www.world-designs.co.uk/forum/sh ... .php?t=689

Looks like you are right Greg.

The only difference between the ones in the pic, on the WD thread and (for the moment

) Martin's are that Martin's have two bright nickel plated end bells, and are upright mounts, rather than drop-through with the single chrome cover.

Greg · Post by **Greg** » Thu Dec 19, 2013 10:30 am

SteveTheShadow wrote:The only difference between the ones in the pic, on the WD thread and (for the moment ) Martin's are that Martin's have two bright nickel plated end bells, and are upright mounts, rather than drop-through with the single chrome cover.

That would be right Steve as they came originally from John Caswell. Although he built most of the WAD kits, he simply bought just the components he needed and used other stock including chassis' he already had. He dislikes drop through Tx's and always surface mounted them with double end bells fitted. Mine came from him are exactly the same.

Cressy Snr · Post by **Cressy Snr** » Thu Dec 19, 2013 3:27 pm

EF50s, VR150s, VR108s and 8 off octal sockets arrived this morning so the basics are now in my hands.

Here is the power supply.
It uses bits I already have in stock.

Nothing fancy; it is proven to work, silently in the existing amp
Only addition to my usual practice is the simple 60 second soft start circuit for the output valves.
It protects the 2200uF, ultra-low ESR, EPCOS
capacitor from over-voltage during startup and ramps up the HT in two easy stages.
Nice and civilized.

ed · Post by ed » Thu Dec 19, 2013 5:25 pm

no limiters on the gz32 anodes?

isn't 47uf a bit strong then?

still, if that's what works already then forget I mentioned it.

Cressy Snr · Post by **Cressy Snr** » Thu Dec 19, 2013 5:38 pm

ed wrote:no limiters on the gz32 anodes?

isn't 47uf a bit strong then?

still, if that's what works already then forget I mentioned it.

Where GZ32 came from I don't know, I don't even own one <proofread you fool>

Should be a GZ34 in that position. <dumbass>

Cressy Snr · Post by **Cressy Snr** » Thu Dec 19, 2013 6:39 pm

Corrected PSU with the right rectifier valve.

andrew Ivimey · Post by **andrew Ivimey** » Thu Dec 19, 2013 9:04 pm

Yeah but no but.... a sweet old mullard gz32 is so much better than a skanky modern gz34.

Deco-Doctor · Post by **Deco-Doctor** » Fri Dec 20, 2013 6:25 pm

This is a good read about the history of the EF50.

http://www.dos4ever.com/EF50/EF50.html

audio-talk

Ideas For EL34 Pentode Push-Pull Amplifier

#61

#62

#63

#64

#65

#66

#67

#68

#69

#70

#71

#72

#73

#74

#75