new project started, 6550 pp monoblocks

Berndt · « **on:** 10 Jun 2011, 09:32 pm »

Hi guys, working with Edwin Yang from the Randall museum DIY audio group. Just finished a set of chassis plates for the prototypes of Edwins new amp project.
Edcor iron, 6550 pp, 6sl7 phase splitter, ef806 driver, and 5u4 rectified.
I think Edwin is planning on using the ampex 6973 circuit that we are using for my 6v6 amp.

Will keep you guys updated, if this sounds decent there will be a Randall museum amp class.

Berndt · « **Reply #1 on:** 10 Jun 2011, 09:34 pm »

Oh yeah, Josh and Tuan, I haven't forgotten about you guys.
This is going to be a good month for turntable parts...

JoshK · « **Reply #2 on:** 11 Jun 2011, 05:16 am »

Very cool project! What made you choose this lineup? Did you follow a particular schematic?

Specifically what made you choose the 6SL7 as a phase splitter?

Berndt · « **Reply #3 on:** 11 Jun 2011, 05:51 am »

Thanks Josh.
This is really Edwins baby, all I can do is parrot what I remember him saying.
First off, Edwin is cheap, and wants to build a cheap, easy to build, good sounding amp that he can teach a class around.
We already have the 6sl7 being used in the Randall phonostage stage, as well as the ef806 being used in the Randall linestage, both of these use the same 5u4 ps.
Edwin is a 300b guy but a lot of people just want more power.
He had been given some console pulls that were the ampex 6973 pp monoblocks, that actually sounded quite nice. These used a long tail cathode follower design with an ef806 driver and a 12au7 phase splitter.
Edwin says the 6550/Kt88 could use more current swing. Also, thanks to you, I believe, we found the cheapo great sounding Russian 6sl7 equivilant that is quiet enough for a phonostage stage and cheap.
So, the 6sl7 is the idea for the phase splitter.
We will see.
I'll keep the progress reports coming.

Berndt · « **Reply #4 on:** 16 Jun 2011, 01:25 am »

Basic bolt up.

Berndt · « **Reply #5 on:** 14 Aug 2011, 11:05 pm »

Test and tune. Pretty big sound, clean bass, wide and tall soundstage.
This is with lowbuck output tubes and opts.

Ericus Rex · « **Reply #6 on:** 15 Aug 2011, 12:43 pm »

Do you have a link to info on this amp? Or others buy this designer?

HT cOz · « **Reply #7 on:** 15 Aug 2011, 01:23 pm »

Check this out http://baasnotes.com/blog/2010/08/25/new-diy-class-next-january/

Berndt · « **Reply #8 on:** 22 Nov 2011, 08:18 pm »

http://www.audiocircle.com/index.php?topic=100809.msg1017638;topicseen#new

Berndt · « **Reply #9 on:** 22 Nov 2011, 08:19 pm »

BTW, I'm going to be building a set of these amps. The beta diyer build.
Probably use Eliano iron.

Berndt · « **Reply #10 on:** 12 May 2012, 04:40 am »

Ok, now the major tweaking is done. I am doing the beta build now.
This is my last bit of copper from my stash. Ended up with Heyboer power transformers and Edcor output transformers.

Berndt · « **Reply #11 on:** 12 May 2012, 04:43 am »

Just waiting for the Edcor ps chokes and opts to start slinging solder.

Ericus Rex · « **Reply #12 on:** 12 May 2012, 12:56 pm »

Gonna be absolute beauties! The glow of the tubes against that copper will be stunning!

Freo-1 · « **Reply #13 on:** 14 May 2012, 10:05 pm »

Very cool indeed! Let us know how it sounds when you finish.

I'm putting together the bits needed to make a pair of 1625 mono blocks, with 12SN7 input/driver tubes.

siliconray · « **Reply #14 on:** 23 May 2012, 12:11 pm »

That's a nice looking amp. Just feel a bit odd to place the RCA and speaker cable connectors on teh top plate.

JoshK · « **Reply #15 on:** 27 May 2012, 12:03 am »

Very cool! Looks like great fun! Do you know what class the outputs run? Been really wanting to build a class A2 PP triode set of amps. KT88s or 6CB5As seem naturals.

jerryleefish · « **Reply #16 on:** 27 May 2012, 02:23 am »

Some thoughts about your project. They look great. I've been involved with Ampex products over time but never had any of their power amps. They did offer amps and speakers in cases to match their recorders. I do have 351 recorder preamps which have 12Ax7 in push pull out put. They are great and offer balanced/unbalanced input option.
I use Luxman 3045s power amps that I modified for 6550s. They sound great and are reliable. I use them with cooling fans.
I've been to a Randell Museum in SanFrancisco. Is this the one you referred to?

Berndt · « **Reply #17 on:** 27 May 2012, 03:55 am »

Yes, the Randall in sf.
If you sign up with them you can get their newsletter.
I built my pre and phono stage there too.
I believe this is class a operation, but I don't know for sure.
The 6973 ampex is a underground cult monoblock in some circles.
Edwin Yang, the amps designer,uses a highly modified drd300b amplifier for his regular runner. Just to give you an idea of what he looks for in an amp signature.

jerryleefish · « **Reply #18 on:** 27 May 2012, 01:36 pm »

Thats so odd. I thought it was for kids only. The first time we went there I pushed my grand daughter up the huge hills from from Market Street. Nobody could believe it. Thanks for your reply.

My first power amp was a Wiiliamson Ultralinear kit from an Allied catalog. It had a separate power supply chassis and used 807s distinguished by anode terminals on top. They were OK but oscillated above 14 watts. I just saw one on Ebay.

Berndt · « **Reply #19 on:** 14 Sep 2012, 03:56 pm »

Fired up the slow this Saturday. Beta builder. First set of amps I've built. Happy with the sound.
They are quiet, and detailed without any hardness. Really big soundstage, great front to back imaging.