Aikido driver into an Interstage in Parafeed

[Andrew]

Hi James,

Build two amps you're incouragable.....

Been thinking....seems like I have half the parts for two amps, if you see what I mean.....

The ouput TX was originally designed for a 300B so that's an easy choice.

The main PSU is good for both.
The driver PSU is good for the PT15 using an E180F (triode or pentode) or a5842
The bias PSU goes with whoever get the ITX.

Obviously, I need a new PSU for the Aikido and eventually an OPT for the PT15.

This little lot will keep me busy for the next 18 months.....

cheers,

-- Andrew

[James D]

For the PT15 some good quality but cheap parts to get you going before ordering Tribute or AE silver amorphous stuff are the AskJanFirst stuff.

Specifically the ATRA0247 output transformer a 5.2K 50mA jobbie that costs €34 each! And they are good.

Jan does some excellent psu trannie to starting at €22 each. And good cheap chokes and caps and resistors...etc etc...

No reason not to do it then

ciao

James

[Andrew]

Hi James,

Still planning and debating here.

The basic problem I have, is that the PSU, which is already part built, is designed for a 5842 into an interstage into a 300B. However, as I said I don't think this will have enough drive to really get the best out of a 300B. The 5842 is a nice "one-valve" solution but input sensitivity is 1.4v

For reference the circuit is the SJS 108IT, the PSU is quite some beast, and one per channel, which is why I wanted to re-use it. Two mains TXs, 3 u-frame chokes and one massive choke for the power valve plus three separate rectifiers.

I have been playing with the hybrid you suggested, which seems like one way to make a single PSU work, but then again, I would like two amps; it would be nice to have a second system for the "study"! But do I need two amps with PSU's like the SJS 108IT? Then again, I can imagine an Aikido 300B would be no less if I did it properly.

But, to make an Aikido 300B happen I might be better off with a new PSU.

So I'm going to forge ahead with the SJS design first. I'll try the both the 300B and the PT15, for the PT15 I'll definitely follow your advice and make use of some of those E180Fs I bought cheap. If I like the PT15 then its a keeper.

But, I'm still attracted to the 300B as an every day user as it's easy to get good replacement valves and I have to say, I'm no valve collector.

And, for the 300B Aikido I'll need to spec a new PSU so that I can get more like 400V for both the Aikido and the 300B. I must say I was drawn in by that vacuum rectification of the SJS design but for an every day user I might be tempted to go for solid state rectification.

Anyway, what sort of operating point should I be looking at for the E180F? If I draw 10mA from my existing PSU and shunt 10mA to ground I get a B+ for the E180F of around 170v. (The original 200v now appears optimisitic doesn't it!).

cheers,

-- Andrew

[steve s]

Originally Posted by Andrew

Hi James,

Still planning and debating here.

The basic problem I have, is that the PSU, which is already part built, is designed for a 5842 into an interstage into a 300B. However, as I said I don't think this will have enough drive to really get the best out of a 300B. The 5842 is a nice "one-valve" solution but input sensitivity is 1.4v

For reference the circuit is the SJS 108IT, the PSU is quite some beast, and one per channel, which is why I wanted to re-use it. Two mains TXs, 3 u-frame chokes and one massive choke for the power valve plus three separate rectifiers.

I have been playing with the hybrid you suggested, which seems like one way to make a single PSU work, but then again, I would like two amps; it would be nice to have a second system for the "study"! But do I need two amps with PSU's like the SJS 108IT? Then again, I can imagine an Aikido 300B would be no less if I did it properly.

But, to make an Aikido 300B happen I might be better off with a new PSU.

So I'm going to forge ahead with the SJS design first. I'll try the both the 300B and the PT15, for the PT15 I'll definitely follow your advice and make use of some of those E180Fs I bought cheap. If I like the PT15 then its a keeper.

But, I'm still attracted to the 300B as an every day user as it's easy to get good replacement valves and I have to say, I'm no valve collector.

And, for the 300B Aikido I'll need to spec a new PSU so that I can get more like 400V for both the Aikido and the 300B. I must say I was drawn in by that vacuum rectification of the SJS design but for an every day user I might be tempted to go for solid state rectification.

Anyway, what sort of operating point should I be looking at for the E180F? If I draw 10mA from my existing PSU and shunt 10mA to ground I get a B+ for the E180F of around 170v. (The original 200v now appears optimisitic doesn't it!).

cheers,

-- Andrew

andrew i would.. say don't waste your money on the 300bs.. and dont worry about pt15 failures.. they will last for years.. my amp sounds really good, it has everything.. i would compare to px25...and much, much better than the old px4 amp ( I'm not saying better than the px4 valve ) i had.. really good bass and top end..but the detail..
use something like a mh41 to drive it.. or ml4 x 2... save the silly little E180f's for a phono or something... or even better make some test equipment with them..

the pt15 is too good not to use!!

all the best...steve

[Andrew]

Hi Steve,

You've played me at least three of your amps all using valves I've never even heard of all, and sounding very very good indeed.

And....on paper, it all sounds such a good idea but.....what I meant when I said "I'm no valve collector" is that I don't have your (or Paul's) patience, and more importantly knowledge nor time etc to hunt and track down such items....your skills in incovering these lost gems has to be applauded.....for my part all I've got is half a dozen E180Fs and no idea what to do with them... ;-)

cheers,

-- Andrew

PS. You dead right by the way...the E180Fs were originally intended for an LCR phono but I'm really happy with my recent phono design and I'm wondering if LCR is worth the cost especially when I still have to sort out my power amp.

[Andrew]

-- Gents,

So I think I'm pretty much sorted, apart form deciding upon a driver stage for the PT15, that is, Steve now having put the cat amongs the pigeons, so to speak. Advice on a good driver for the PT15 is therefore still welcomed.

Anyway, here's the plan....

I have a nice dual mono, valve rectified, PSU that can do ~400v, ~175v and fixed bias should I prefer that to cathode bias for the PT15 amp.

Build the PT15 first, initially using my 300B OPT to get the PT15 going, but use the 4R tap on my 6R speakers.

Try some different drivers, and loading strategies on the driver.

For the 300B Aikido, and this is a bit of a way off, I thought it might be worth trying something a bit different.

I was thinking the brief might be.

Use easy to obtain valves driver valves, keep any esoteric stuff that I source for the PT15.

Solid state rectification, this will keep the cost down and simplify construction no heaters needed for the rectifiers etc. I've been looking at some of those nice hypersoft recovery jobbies, which if properly snubbed, should be just fine. Something like three main secondaries, one for the driver and one for the PSU and one for bias, plus heaters for the driver valves and for the 300B.

Use choke input and LC smoothing, should be able to get between 300v and 400v B+ with no problems. I find choke input is better as the choke draws almost continuous current from the PSU rather than just the peak draw of cap input.

Buy new ironware for the PT15 from someone like AE or Tribute once I have settled on the driver and then liberate my existing OPT and interstage for the 300B.

Re-use my existing interstage in parafeed for the 300B.

Re-use my existing OPT as it was originally designed for a 300B.

Try out Partial Feedback.

cheers,

-- Andrew

[Greg.]

Hi Andrew et al,

A small thought based on my research for the build of my 300B PP clone. If you are going to use quality (boutique) diodes in the PS, do you actually need snubber caps? I left them out of my build. I'd be interested in the opinions of others as long as the question does not take this thread off Andrew's topic.

Best wishes,

Greg

[James D]

Hi Greg,

Short answer is.... it depends

Any solid state diode has some reverse recovery switch - the question is whether it excites any resonances in the psu... if it does then it should be snubbed at source BUT snubbing if not calculated for the specific diode and psu will make the ringing worse not better

So for soft recovery diodes and Sh. I often leave then un-snubbed.

Andrew,

Still thinking on my reply probably post tomorrow.

James

[NickG]

Just a thought, when you mention snubbers, are we talking across the diodes, or the choke, in my understanding, whatever diode you use, the choke needs a snubber, as the diodes will still have a angle during which they will not conduct.

[Greg.]

Hi Nick,

Specifically I was talking about snubbers across the diode bridge. I've not considered beyond that.

Best wishes,

Greg