EMI RS124

[rickc]

the balance point happening at the end of the pot indicates mismatch in the tube sections, as lassoharp indicated.

the balance controls interract, so you have to do one, then the other, until you have the best common-mode null.

Here's a link to follow: http://www.tubebooks.org/hb-3_tube_manual.htm

It's to Pete Millett's site, and the RCA tube handbook (which is not to be confused with their tube manuals) can be found there, painstakingly scanned to individual pdf files. This is the holy grail of tubes.

Every tube has a standardized base designation that identifies the pinout. It's a number and letters. The number indicates the number of pins actually used. The letters indicate the basing.

The 6ES8's base designation is 9AJ, and so is the 6922. But the 6BC8 designation is 9AJ, so they're not pin-for-pin identical. They may be close, however, so it's up to you to figure it out.

FWIW, the 12A*7 tubes are 9A, the 6L6 beam power tubes are 7S.  Sadly, the handbook manuals don't show this. The sylvania manual does however.

Also recommended, navigate up to the root of this site, because there are many, many books there available for downloading, free, no strings attached.
http://www.tubebooks.org/tube_data.htm

and finally, the highest level site: http://www.tubebooks.org/

If you haven't seen this site before, you'll be busy for hours.

 

[gary o]

Thanks Lassoharp yes I suspected my 6K8 already and found it was open circuit also my R7 220R as I only had lower rating ones to hand as I was hashing up the circuit not expecting it to be a permanent project, strange thing was no smoke just open circuit....have replaced them & now all volts are there abouts, other funny thing was the circuit still performed well before not sure how....

Yeah the balance pot......Im not getting any problems with control voltage pops or any thing it compresses well & sounds great at any cathode pot setting, Im slightly worried it works too well ....

I see that ECC88C is not same as 6BC8 unlike fleabay seller says .....its not vari mu, I tried one anyway as its pin compatable it sounds pretty good actually but  my friend sending me a good 6SE8.

Rickc thanks for those links loads of info there that I may need later as I am lucky to have been given boxes of tubes by a friend.

Thanks for your help guys.

 

[JayDubrek]

Hi Gary- have you used the schematic 'Winston' posted for your build? Just been looking over the schematic on Drip's site linked above (drawn by Ladislav Bresovnik) and there seems to be a couple of differences...
On Winston's R12 33k connects to the 6AL5 anodes and the neon circuit while the other side goes to the input TX center tap. On Drips site the input center tap goes straight to the timing network while the 33k resistor (now labelled R26) connects to the output CT.

Anyone care to shed any light?

Thanks
Jay

 

[gary o]

Hi Jay yes I used Winstons schematic I cant see the need for a PCB at all really, I just drilled some holes in some ali and soldered it together no plans took about a day & cost nothing, I learnt as I went Ive made lots of projects this way....... I cant see the link to drip schematic here ......I found a drip schematic via google seems to be quite a bit different, there seems to be many 436/RS124 variants over the years, I made the VK1 circuit & that worked pretty good........are you trying to change a PCB to take Winston circuit.....all I can say is this thing work brilliantly I love it !!

I love the neon oscillator , I have made that separate & want too try in my DIY BA6A too

Let us know how you get on

All the best, Gary O.

 

[haima]

+1 sound advise there Gary 

 

[JayDubrek]

The link is posted via Baadcode on this page...it's to a thread containing a few snippets of info on the rs124. It's going to be a while till I get to this - I'm up to my neck in a console project but I'm still following the thread.... and if someone has posted some possible misinformation I thought it best to check over it...I've seen so many RS124 schematics over the years claiming to 'be the one'! The schem on the Drip forum uses tube rectified power...apart from the differences I mentioned in the last post they're the same.
I'm not modding a pcb and Drips boards are way too expensive...all my tube gear builds have been ptp so far....
You gonna show us some photos then Gary!?
Cheers
Jay

 

[gary o]

Ah I see the link now, it seems to be a Altec 436C & not RS124 .....Jay I see what you mean about the 33K resistor the question is asked earlier in this thread....the capacitor here is different too .1uf on the 436C/drip & .5 on the Winston, but I guess these other little changes that Winston explains change the way this thing works for the better make it a RS124 & not a 436C/drip there quite a few other differences....

Jay I will see if see if I can do a pic but it wont be pretty hehe

 

[JayDubrek]

Yeah I've seen this circuit get twisted round so many ways it would be cool to see and hear one built from Winston's (John Hinson) schematic...
Stick a pic up- I'm twisted enough for some ugly porn! ;-)
Jay

 

[baadc0de]

The 436c with mods from Drip is what it is.. an australian drip forum member brezo modded it to RS124 spec. Anyway, carry on..

 

[gary o]

I might do ugly porn video for you tube....

Im just experimenting with Input transformers at the moment my BA6A wants his 1:4 back now .....

I found a freed 15K/60K CT transformer in my junk box.......that seems to be the original spec for a 436 ?.......I have tried it in circuit it sounds good slightly lower level & maybe less  bass, but maybe due to not making the circuit compress as much due to lower level .....is 15K /60K 1:2 ratio ? I dont quite understand transformer specs....

I was reading that a OEP A262A6E wired as 1:1 could be a good choice.........

 

[gary o]

http://youtu.be/igyyeMIyrkA

 

[Joechris]

Great video, Nice voice, Nice compressor

 

[gary o]

Thanks Joechris as I said still experimenting.....

Disconnecting my input transformer centre tap make no difference so sound or compression .......does that soun correct........I have seen some vari mu circuits without a centre tapped iput tran ....Altec 438 for one .....two resistors being used instead I think......when I disconnect the centre tap on my ba6a it messes everything up ....

 

[Jean Clochet]

Hey Gary,
haven't really been watching this thread so don't know all the details...
But, great job!  On everything. 
Nice DIY on the RS124 circuit, as well as your pre/U-47 mic and great job as well on the 'Hey Jude' vocal.

 

[JayDubrek]

Nice one Gary! And workshop porn too! As Jean said, great vocal...
Anyone else here tried the Winston circuit yet?
Jay

 

[lassoharp]

Anyone else here tried the Winston circuit yet?

Yes.  Just completed a build using it.  Comparing it to the standard 436 circuit, it seems to behave a little better overall in regards to thumping and the problems that creates.  I also like the release arrangement better than the single pot of the original, and the hold function is very handy.  IMO the key with either version is to use it on material that doesn't require an attack time faster than the unit can deliver.  I know that seems obvious bet seldom gets mentioned when comparing the 436/RS124 to other vari-mus.  I've found it great on bass but it can make a mess of close miked acoustic guitar.

 

[DaveP]

GaryO,

What a great voice you have.....Pitch Perfect!

Your workshop is not as bad as you led us to believe, you'd be at home in mine!

Glad you got it sorted.

Jay,

I converted my 436 the same week Winston posted, it works very well and I'm convinced its the genuine article.

I did not build the hold circuit though or the neon tester as I had already spent ages getting it perfectly balanced.

Best
DaveP

 

[JayDubrek]

I built the 436 a couple of years ago and it gets used once in a blue moon....generally on bass guitar! When I eventually get round to this I'd planned to leave out the neon circuit like you have Dave. Which input and output transformers did you chaps opt for?
Cheers
Jay

 

[DaveP]

I built the 436 a couple of years ago and it gets used once in a blue moon....generally on bass guitar! When I eventually get round to this I'd planned to leave out the neon circuit like you have Dave. Which input and output transformers did you chaps opt for?
Cheers
Jay

Jay,

I used Sowter's 3575 for the input and 9745 for the output.

The Beatles only used them for guitars too, as I understand.

best
DaveP

 

[gary o]

Wow thanks for compliments chaps....... Im not really a Beatles fan but I love that song Hey jude and the vocal recording it self... Dave or anyone do you what they used on vocals at the time Hey Jude was recorded.....as I switch the soldering iron on .....

Jay used transformers I had ( in fact the whole thing was made from junk) so maybe not ideal, my output is a Sowter 8650a 6:1 ratio I think, I bought it for a Mccurdy push pull pre amp I made its output valve was ECC82 I hope it might be good match for the RS....

For input I borrowed a Sowter 8540 that Brian sowter sold me for my DIY BA6A before he made the custom ones he now sells, its a 1:4 ratio so has more level & drives the circuit into compression easily & so I use my ratio & pad the output its works well tho I would like to try a 1:1 like dave the 3575....I then found a Freed 15K /60K & I believe thats spec for a 436 1:2 ratio is it ????/ it works well too slightly less bass....

I have been wondering about a cheap OEP262A6E 1:1.....

I  absolutely love this little compressor for vocals more so than LA2As I have built, LA4A and 2 versions of 1176s....its such fun simple circuit to experiment with too I cant seem to get it to pop & thump not that I want it to, but other vari mus seem more sensitive, Im slightly worried but in a good way....