Advise on interstages...

Neal · Post by **Neal** » Tue Apr 22, 2008 9:59 am

Following on from a brief conversation with AndrewI at Owston I now want to experiment with an interstage in my 2A3 PP.

I'd like to eliminate the single cap I have between the long tail phase splitter and 2A3 o/p pair.

So it's L plate time. Never having messed about with interstages from scratch I'm looking for some gudance on where I can get reasonable off-the-shelf items and what to look for.

I'm currently using a 6FQ7 and want to try it in an interstage configuration along with 5687, ECC99 or the 6463....

Thanks!

andrew Ivimey · Post by **andrew Ivimey** » Tue Apr 22, 2008 11:48 am

Hello Neal, if you want to preserve the SE to PP you 'need' a lundahl 1635. If you wantto make the whole thing PP you need input trafo (I use Lundahl 1676) and interstage (1660) I buy from Kevin Carter (K&K audio) He is an extremely knowledgeable and helpful chap and Lundahls are cheaper than Sowter, who also make appropriate trafos.

I've also emailed Bud Purvine about some more metal. His trafos appear to be excellent and reasonably proced. The prob, here can be that it does take time.

I am sure and interested that others will contribute more to this. Max, for example, got his wound especially for his custom design.

If Mr Creswell has given up on his PP experiments I'd really like to experiment with his Sowter 3575 input transformer

steve s · Post by **steve s** » Tue Apr 22, 2008 12:01 pm

I've been thinking the same neal.. i have ben wondering for a while..

but from a single ended perspective.. of course..

you never know until you try it... so i think thats what i need to do..
nearly all they ever used in the 30's.. so right up my street..?

i would guess the quality thing is the same as with output tx's
mostly subtle, but real differences in tone and detail..?

steve

Post by **Nick** » Tue Apr 22, 2008 12:03 pm

I am sure and interested that others will contribute more to this. Max, for example, got his wound especially for his custom design.

Yes, could someone (possibly Max) remind me where those TX's came from, and what was the driver valve again?

andrew Ivimey · Post by **andrew Ivimey** » Tue Apr 22, 2008 12:27 pm

The driver was 5687!

(I started with 6N6P and quickly preferred ECC99. I need more welly as I have less HT and am not using the luxurious 300B. Is there a double triode out there with more welly that ECC99.... 6N30P, I don't know?)

There is an amp design knocking around, see for example the attachment, that I tried with any old 1:1+1 I could find and it sounded good, but then Amity took off and I never went back to it. It shows how easy it is to get started!

Andrew · Post by **Andrew** » Tue Apr 22, 2008 12:37 pm

Nick wrote:
I am sure and interested that others will contribute more to this. Max, for example, got his wound especially for his custom design.
Yes, could someone (possibly Max) remind me where those TX's came from, and what was the driver valve again?

Moorite to an Andy Grove winding spec. Driver was a 5687

Cressy Snr · Post by **Cressy Snr** » Tue Apr 22, 2008 4:23 pm

andrew Ivimey wrote: If Mr Creswell has given up on his PP experiments I'd really like to experiment with his Sowter 3575 input transformer

Hi Andrew,

PM me your address and I'll send them on to you.
The Sowter 3575 makes a good IPTX/phase splitter. Probably not up to the standard of the Lundahls but superb for the price.

Steve.

Neal · Post by **Neal** » Tue Apr 22, 2008 4:43 pm

Thanks for the input Guys,

Yes, Max was using the interstages we had designed and wound by Morite. They where designed for a pair of 5687 in PP driving PP into the 211's. I want to stick with SE into PP for now so will check out Andrew's Lundahl suggestion, thanks!

Neal · Post by **Neal** » Tue Apr 22, 2008 4:55 pm

Interesting, I just checked the Lundahl site and the 1635 is not recommended for SE driver into PP, the 1660 is though...

andrew Ivimey · Post by **andrew Ivimey** » Tue Apr 22, 2008 5:24 pm

Odd indeed because, to a simple soul like myself, that is exactly what a 1635 is for. A 1660 is more versatile as it will do either SE or PP.

pre65 · Post by **pre65** » Tue Apr 22, 2008 9:27 pm

Hi-try the Bluebell web site for details of a 2A3 interstage amp that Philip built and is now for sale.See under "sale items"

to quote ---5842 input Triode, transformer coupled 1:1 - SE 2A3.

Choke input power supply L.C.L.C. filter.

Fixed bias with trim pots and test point sockets.

"I built this up over Easter to try out the new Hammond 126B IT . This offered up the chance to use the 302AX pwr Tx in choke input mode with a separate bias supply. The overall sound is smoother than the standard Loftin-white circuits I usually build. The 250v B+ is rock solid and delivers a very impressive sound-stage for the 3.5watt output"

This type of amplifier is best driven from an Active pre-amp.

For more information call Philip on 01382 221959

http://www.bluebellaudio.com/

andrew Ivimey · Post by **andrew Ivimey** » Tue Apr 22, 2008 9:42 pm

No, no no and seriously no, Philip. Mr Ramsey may have some stonkingly good interstages but they are SE only. They really wouldn't work for SE into PP.

I'm still holding my breath for Mr Counter to finish his 2A3SE interstaged amp - should be a good'un.

As I already have some cheap american and hongker appropriate interstages I'm going to take apart my Bluebell designed 2A3PP amps and convert them to the design I posted a while back. I've got quite a few 5482 / 417as too so it should be a doddle and I'd like to take time to appreciate this design.

david C · Post by **david C** » Tue Apr 22, 2008 10:26 pm

Philip is impressed with the interstage 2A3, I am yet to finish mine so I can't comment yet, if it's as good as Philip says I'll be well impressed,

the interstages are good value but as Andrew said only good for SE

Will · Post by **Will** » Wed Apr 23, 2008 12:09 am

The 5842 I/T 2A3 in SE seems on paper very worthy but not up the standard we had at Owston Ive built it and its IMO not worth the effort.
Sorry to be blunt but the marriage between the valves was made in hell.
I say little and folks should always find there own way into sounds but not with this.

Post by **Nick** » Wed Apr 23, 2008 12:33 am

Sorry to be blunt but the marriage between the valves was made in hell.

Blunt is good Will, I have no opinion on this as I haven't been there, you have, so shout out.

audio-talk

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