synthi

Another vari-mu: Chiswik Reach Compressor
« on: November 29, 2005, 08:12:16 AM »
Hi People!
I just scored this beauty:


It´s a very early VK1 compressor, Serial #14. I`ve told this design is based in the altec (emi) compressor.
The tubes are:
1x 5AR4
2x 12AT7
2x 6BZ7
2x 6AL5

I need to revalve and adjust the unit, the channels are not matched and the tubes about to die... just changed the 12AT7s (the only tubes I had) with a matched pair the channels are more equal in gain, but I`ll need to replace all the tubes.

the 5AR4 is the rectifier, no problem, the 6AL5s I think are sidechain rectifiers (?) and the 6BZ7 the variable mu tube :?:

I want to get a pair of matched pair for each but nobody seems to sell matched pairs of those, so:
-Can anyone sell me a matched pair?
-Or... I could get some of each (10-15) but what values must I look for match the vari-mu tubes (and rectifiers)?

Here is a link to the new compressor manual (almost the same thing, different trafos):
http://www.jivelive.com/chiswickreach/assets/images/manual2.pdf

Now here is some p*rn, the circuit is all point-to-point and seems simple enought to be useful from the photos:






Thanks!

Synthi.


Another vari-mu: Chiswik Reach Compressor
« Reply #1 on: November 29, 2005, 08:27:33 AM »

synthi

Another vari-mu: Chiswik Reach Compressor
« Reply #2 on: November 29, 2005, 09:02:59 AM »
:shock:  So the phoenix is based  on the chi*wik! And also Vic Keary was the designer for my unit :)

I`ve found more info here:

http://www.thermionicculture.com/reviews/review_monitor_phoenix.htm

The 6BZ7 used in my unit seems to be a replacement for the original 6BQ7A, so I`m gong for a matched pair of the 6BQ7As. What about changing to PCC85 as mentioned in the article? is a direct sub?

Thanks!

Synthi.

Viitalahde

Another vari-mu: Chiswik Reach Compressor
« Reply #3 on: November 29, 2005, 10:36:37 AM »
Dare I say?

REVERSE

ENGINEERING

WANTED!!!

 :grin:  :grin:  :grin:

Nice photos!

synthi

Another vari-mu: Chiswik Reach Compressor
« Reply #4 on: November 29, 2005, 10:46:20 AM »
hehehe :grin:

If anyone is going to R-Eng I can provide detailed photos at your request!
 :cool:

Thanks,

Synthi.

Another vari-mu: Chiswik Reach Compressor
« Reply #5 on: November 29, 2005, 12:02:53 PM »
From that SoS Review
The Phoenix was the first of Thermionic Culture's products, and its design derives in part from the Altec 436 'vari-mu' compressor. This used 6BC8 triodes in a balanced (push-pull) configuration, but produced what Vic felt was unacceptably high distortion, so he improved the design during his time at Chiswick Reach, and it became known as the Chiswick Reach compressor (reviewed in SOS in February 2000; see www.soundonsound.com/sos/feb00/articles/chiswick.htm). However, the noise floor was still not as low as Vic wanted, and further development eventually resulted in Thermionic Culture's Phoenix compressor (see www.soundonsound.com/sos/apr00/articles/phoenix.htm). Some of the noise-floor improvement came from changes to the power supply, but some also came from a redesigned front-end which used a PCC85 valve instead of the Chiswick Reach's 6BQ7A. The PCC85 tube was designed for FM radio applications and hasn't been used in an audio application before; it requires an unusual 9V heater supply. However, all these cumulative changes brought the overall noise figure below -100dB, improved distortion further to 0.1 percent, and enhanced the general reliability of the compressor. Vic also improved the machine's flexibility and performance over the Chiswick Reach design with faster attack and release times. As this history shows, Vic is an inveterate tweaker, and still feels there are advances to be made with valve technology. He is currently experimenting with a different output valve for the Phoenix.


rafafredd

Another vari-mu: Chiswik Reach Compressor
« Reply #6 on: November 29, 2005, 11:08:53 PM »
Quote
If anyone is going to R-Eng I can provide detailed photos at your request!


Man, it looks easy!

Come on!

CJ

Another vari-mu: Chiswik Reach Compressor
« Reply #7 on: November 30, 2005, 12:08:17 AM »
Holy Cow I just threw out about ten of those BQ7's because I had so many of them!  Or was it BK7?

Also, 6AL5's out the wazoo, but Spain pays the shipping.

Andy is trying to get a socket that fits so he is cleaning out the house.

Dude, it's like, I couldn't see out the back window. I bought an HS-29 and a WeCo 111C and he "threw in" over 1000 tubes, in the boxes, yo.
 :thumb:

Don't feel sorry for Andy, his place looks the same, even after 5 or 6 carloads of stuff taken out. Barley even put a dent into that place. If there was a drive by, they would never find the bullets!
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

NewYorkDave

Another vari-mu: Chiswik Reach Compressor
« Reply #8 on: November 30, 2005, 09:24:48 AM »
Too bad about those 6BQ7/6BZ7s: they're good for cascode amps--and so are 6BK7s, as a matter of fact. Let me know if you need to get rid of any more :wink:

ciminosound

Another vari-mu: Chiswik Reach Compressor
« Reply #9 on: November 30, 2005, 09:35:52 AM »
It would be great to see the schematic for this. I have a bunch of the BC8, Bq7, Bz7. (They are listed as subs for each other in most books)

Curious about the Pcc85 though.  Isn't that a different heater Ecc*85? Ecc*85/ 6*A*Q*8? This tube type has been used in audio quite a bit.


gyraf

Another vari-mu: Chiswik Reach Compressor
« Reply #10 on: November 30, 2005, 09:47:20 AM »
I suspect that the tubes are the least esoteric things about this piece. I count at least five transformers / inductors.

Other than that, it looks pretty much like the prototype for my G10..  :razz:

Jakob E.
..note to self: don't let Harman run your company..

synthi

Another vari-mu: Chiswik Reach Compressor
« Reply #11 on: November 30, 2005, 09:52:12 AM »
There are 2 input and 2 output trafos, a mains trafo and the smaller one near the mains may be a 6.3V trafo?

Synthi.

Another vari-mu: Chiswik Reach Compressor
« Reply #12 on: November 30, 2005, 10:57:03 AM »
I found this interesting...
The gain-reduction meters are not just VU meters modified for the task, but actually show the cathode current of the 6BQ7 gain-controlling valve. As the performance of these valves alters with age, it becomes necessary to trim the meter circuit, for which purpose a pair of electronic zeroing trimmers has been provided in the centre of the front panel

Transformer detail


substantial custom-designed devices, which apparently won't saturate below +24dBu, suffer only one degree phase error between 10Hz and 25kHz, and exhibit -3dB points only at 4Hz and 35kHz. Impressive beasts indeed, and fully shielded with mu-metal
published specifications quote distortion as better than 0.08 percent with +8dBu input level and 5dB of compression

And found this nice comment

Sowter transformers are used throughout Thermionic Culture's products ? both for audio and mains

synthi

Another vari-mu: Chiswik Reach Compressor
« Reply #13 on: November 30, 2005, 11:04:14 AM »
Does anyoneone the contact info for the thermionic culture technical service or Vic himself?
in the website the only email is for the distributor...

Synthi.

NewYorkDave

Another vari-mu: Chiswik Reach Compressor
« Reply #14 on: November 30, 2005, 11:05:30 AM »
Quote

The gain-reduction meters are not just VU meters modified for the task, but actually show the cathode current of the 6BQ7 gain-controlling valve.


Big deal. That's how it's almost always done in "vari-mu" compressors.

Quote

substantial custom-designed devices, which apparently won't saturate below +24dBu, suffer only one degree phase error between 10Hz and 25kHz, and exhibit -3dB points only at 4Hz and 35kHz. Impressive beasts indeed, and fully shielded with mu-metal


Except for the mu-metal shielding, a $9 Edcor can meet those specs--at least in terms of maximum level and frequency response. I'm suspicious of that quoted phase shift figure, unless the xfmr was tested under some pretty un-realistic conditions.

I'm sure it's a fine compressor, and I'm not trying to piss on anyone's parade, but don't make the mistake of thinking that any given set of specs are remarkable just because the copy-writer wants you to believe that they are :wink:

synthi

Another vari-mu: Chiswik Reach Compressor
« Reply #15 on: November 30, 2005, 11:14:30 AM »
Quote
Except for the mu-metal shielding, a $9 Edcor can meet those specs--at least in terms of maximum level and frequency response.

I'm sure it's a fine compressor, and I'm not trying to piss on anyone's parade, but don't make the mistake of thinking that these specs are remarkable just because the copy-writer wants you to believe that they are


Yes, I know, but the question is that would be a good vari-mu and seems to be easy enought to clone... or even improve!

Synthi.

gyraf

Another vari-mu: Chiswik Reach Compressor
« Reply #16 on: January 04, 2006, 04:10:37 AM »
Nice drawing, Olaf!!

 :thumb:

Jakob E.
..note to self: don't let Harman run your company..

t-wurst

Another vari-mu: Chiswik Reach Compressor
« Reply #17 on: January 04, 2006, 04:42:18 AM »
Just read this topic and my first thought was "Oh, looks like the Phoenix"!
Reading further this thought was proofed - funny  :grin:

I made some shots while Mr. Brauner himself (you know, this german microfone-guy) put his Weller-Iron in our Phoenix to change a defective switch. Try to upload these pictures soon. They´re using SOWTER xformer and Siemens Valves and the same "easy" point to point wiring - and the same housing...

Post pics soon

chrissugar

Another vari-mu: Chiswik Reach Compressor
« Reply #18 on: January 04, 2006, 05:36:33 AM »
Are you sure the output transformer is 9745?
I looked at Sowter for this transformer and it looks totally diferent. I compared the 9745 pic with the third pic in your first post.

chrissugar
Christian Mike Sugar
        CMS-LAB

chrissugar

Another vari-mu: Chiswik Reach Compressor
« Reply #19 on: January 04, 2006, 05:47:04 AM »
OK, now I'm confused.
If I do a search on the Sowter page it gives diferent picture, but if i look for the 9745 at "PRO VINTAGE" it looks like the transformer is an M6 with U clamp (like in your pictures).
Probably the picture at Sowter in search mode is wrong.

chrissugar
Christian Mike Sugar
        CMS-LAB


 

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