the pimp / mod the Poor Man 660 thread

[bluebird]

Yes I'm using the Jensen backwards for the input transformer. This is really not a significant mod. the edcors are great transformers.

And yes, I am now VERY excited about how this sounds now.  ;D

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap. You don't really have to change the cap value to get a good variation of release times. It has a lot more effect than the stock 10K pot in series with the 10uf cap.

 

[Gachet]

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap.

What value?
I couldn't find it....

 

[flintan]

Anyone know what the U-pad in front of the SC amp transformer is for? Talking about the original here.

 

[emrr]

Anyone know what the U-pad in front of the SC amp transformer is for? Talking about the original here.

isolation

 

[khstudio]

Yes I'm using the Jensen backwards for the input transformer. This is really not a significant mod. the edcors are great transformers.

And yes, I am now VERY excited about how this sounds now.  ;D

I wanted to mention an easy way to get a good range of time constants without big changes is to just use the resistor values I mentioned earlier in parallel with the 10uf cap. You don't really have to change the cap value to get a good variation of release times. It has a lot more effect than the stock 10K pot in series with the 10uf cap.

Is the 10k pot in Series (Original setup) still needed or usable along with your parallel values?

Also, how does the original "Series" pot setup even affect the "Release"???
I'd think it would mostly control the "Attack"... no?

Sorry, I'm designing my face-plate & I'm trying to get a grip on the "Time-Constant" debate/choices before I Drill holes & move forward.

 

[Moby]

Also, how does the original "Series" pot setup even affect the "Release"Huh
I'd think it would mostly control the "Attack"... no

Yes, series resistance determines the attack time (cap charging) . If you want to add proper names under the switches, my advice will be that you  call switch with capacitors as time constant and parallel resistance as release. Not 100% true but close to be true  . Yes, series resistance with C's can be useful (see the Fairchild) but is gonna take some to determine value and position. (I still don't know my values  :-\)

 

[flintan]

Anyone know what the U-pad in front of the SC amp transformer is for? Talking about the original here.

isolation

Hmm.. Isolation from what? The channels interacting with each other in lat/vert mode or something else?

 

[emrr]

Isolation between the side chain amp and the audio output/following input.  Many vintage broadcast and recording amps use resistive build out as part of isolation networks.  In many cases to help fix the load Z range while providing a degree of isolation with situations such as phone line connection during remote broadcast work. 

Also sets audio amp load Z range; can't comment since don't know sec Z of side chain input.    Situation is similar in regards to the PM660 as to isolation, different in regards to load Z range.  One would ideally assume the values of input load shunt were tweaked for best response in each. 

 

[bluebird]

Hey, just a little update on the bluebird mod...

I've scaled back to three caps. 10uf, 6uf, and 2uf.
Also using just three resistors in parallel with the caps. 68K, 470K, and 3m (or no resistor).
With those caps and resistors you can simulate the first three or four time constants of the real 670.

I ended up cranking the power supply up to about 210 volts and using four 6BA6's per side. I matched the 6BA6's up with a tube tester. I wired two 6BA6's  to a 9 pin tube socket with buss wire kind of like the Manley T bar to eliminate some oscillation I was getting earlier when using  4 inches of wire from the 7 pin tube sockets to the 9 pin tube socket. Both adjustment points are at 7 volts.

The power supply seems to be handling 8 6BA6's fine. I just changed one resistor (R9 to 470K...) in the power supply to up the voltage. I do have 2 fans in my box. I feel like I'm over clocking a PC or something..

New mod....

I changed the input a bit
I took the jensens out and put the edcors in for the input transformers.

I removed the input attenuator and hooked the input transformer secondary right up to the grids of the 6BA6's. I attached the CV voltage to the center tap of the input transformer like on the original 660.
I used a 600 ohm T attenuator in front of the input transformer.

It sounds better to me now... ;D

 

[Moby]

Hey, just a little update on the bluebird mod...

hehe a little  ;D

 

[bluebird]

Just wanted to comment on the tube change.

The whole reason I did all this is because I wanted more gain reduction than the original circuit could provide. The 6BC8's are cool tubes for compressors. The UA175 is possibly the best sounding varimu out there. A company makes a reissue of the UA175 that people go nuts over.

BUT for this compressor they dont seem to like being pulled down to far.

I think the reason the 6386 tube is so special is because the grid wire is wrapped around the support posts non linearly. The wraps get wider towards the middle of the support posts. kind of like a ladder with a couple of steps missing from the middle. I had a chance to talk to a tech here in LA who has worked on over 100 Fairchilds and he told me about the 6386. So I busted open (CJ style) a 6BA6 an sure enough the grid was wound non linearly. So now I know why the curves are similar between the two tubes.

Picture of a 6BA6 grid

 

[emrr]

The UA175 is possibly the best sounding varimu out there.

I busted open (CJ style) a 6BA6 an sure enough the grid was wound non linearly. So now I know why the curves are similar between the two tubes.

Good man!  Cracking open a tube.  Thanks for the pic.

To register another opinion (remember, like ********  ), I never found any use whatsoever for the several UA 17x series limiters I had access to.  Always unplugged them and went with something else.  Among the vari-mu types here I count Collins 26U, Gates SA-39, Gates 28-CO, RCA 96, RCA PA-136, and have had GE Unilevels, Gates Stalevels, RCA BA-25's and Langevin Levelines.    I tend to think people flip out over the units with the most control range (attack/release/threshold/output), and I find that there are simple range expansions that can be done to all of the relatively 'control-less' types listed above.  I know the UA has more control range than the others right out of the box, and have to think that is why so many people like them so much. 

 

[joe-electro]

Among the vari-mu types here I count Collins 26U, Gates SA-39, Gates 28-CO, RCA 96, RCA PA-136, and have had GE Unilevels, Gates Stalevels, RCA BA-25's and Langevin Levelines. 

Enough bragging! We want gear ****!!!! Especially the RCA 96 and Gates 28-CO! Got any pics of the Levelines?

Sorry for the off-topic post.

---Joe

 

[analag]

I think it's time I posted on this here thread....there is another pimp, but it involves way more than just turning up the regulator and changing tubes. Then it's no longer the Poor Man 660 is it.

 

[bluebird]

Hey Analag bust it out... It can be called the Pimp Poor Man 660 Or the "PPM 660

I was thinking I might try throwing in a couple of the new 6386's with some socket converters but other than that I can't think of much else to do to this thing. I'm really digging what this is doing to vocals and drums on the 2uF and 68K setting. Its starting to be my go to compressor.

What might make it better is to get a little more out of the sidechain amp. I might try using the center tap and one side of the secondary of the sidechain output transformer into the bridge for more current drive. More of a step down. BUT that would mean less threshold voltage.

To register another opinion (remember, like ********  ), I never found any use whatsoever for the several UA 17x series limiters I had access to.  Always unplugged them and went with something else.  Among the vari-mu types here I count Collins 26U, Gates SA-39, Gates 28-CO, RCA 96, RCA PA-136, and have had GE Unilevels, Gates Stalevels, RCA BA-25's and Langevin Levelines.    I tend to think people flip out over the units with the most control range (attack/release/threshold/output), and I find that there are simple range expansions that can be done to all of the relatively 'control-less' types listed above.  I know the UA has more control range than the others right out of the box, and have to think that is why so many people like them so much.  

Understood. Do you like the Altec 436C ? that also uses a 6BC8, my point is the 6BC8 is not a bad tube for varimu work, But in this circuit it doesn't seem to like being hooked up to the load...or something. Everywhere else I see it the next stage is a tube grid.

Sound is so subjective anyways. I try to refrain from being to creative explaining the way something sounds.

I don't want someone to go through all the trouble of doing what I did to a piece of gear and then go "damn this sounds like ****".
But on the other hand this whole forum is about experimentation and learning from our (and others) mistakes.

 

[Moby]

Analag, do I smell a JJ6386 around 

 

[joe-electro]

I think it's time I posted on this here thread....there is another pimp, but it involves way more than just turning up the regulator and changing tubes. Then it's no longer the Poor Man 660 is it.

Okay, enough teasing, out with it!!!

---Joe

 

[emrr]

Do you like the Altec 436C ? that also uses a 6BC8, my point is the 6BC8 is not a bad tube for varimu work, But in this circuit it doesn't seem to like being hooked up to the load...or something. Everywhere else I see it the next stage is a tube grid.

Been a long time on the 436; don't remember being wowed, and never considered getting one after they shot up so high. 

 

[joe-electro]

Enough bragging! We want gear ****!!!! Especially the RCA 96 and Gates 28-CO! Got any pics of the Levelines?

Not trying to brag, just establish a baseline for my experience.    Not many good pics.  Here's some OT bandwidth hogs:

Collins 26U-2 stereo limiter with added control panel
Collins 26U-2
Collins 26U-2 with back open
Collins 26U-2 stereo limiter with top open.
Collins 26U-2, close-up of PSU recap using perfboard and radial caps
Collins 26U-2, bottom view showing wiring to added control and connector brackets
Collins 26U-2, with added bottom panels and significant control set modifications.
Collins Radio 26U-2, shown in limiting and below threshold, with stock slowest attack and fastest release.

RCA BA-25A rack-up; front
RCA BA-25A rack-up; top
RCA BA-25A rack-up; rear
RCA BA-25A tubes
RCA BA-25A guts
RCA BA-25A rack-up. Someone else started this one; I changed a bunch of stuff and got the cosmetics happening. 
RCA BA-25A rack-up; controls
RCA BA-25A rack-up rear
RCA BA-25A rack-up guts
RCA BA-25A rack-up; bottom showing PSU changes including DC filaments

RCA PA-136 front 
RCA PA-136 top 
RCA PA-136 side 
RCA PA-136 guts
RCA PA-136 showing amp disassembly from rack and wiring harness. The amp rotates from a pivot point while in the rack of access to top and bottom without full removal.  Can be powered with AC or DC with change of jumpers.

Gates 28-CO limiter front before restoration.  Note totally incorrect knobs.
Gates 28-CO limiter rear before restoration
Gates 28-CO limiter bottom before restoration

Gates SA-38A with modified attack and release controls 
Gates SA-38A, open 
Gates SA-39 with modified attack and release controls
Gates SA-39 rear 
Gates SA-38 with attack and release control modification
Gates SA-38, door open
Gates SA-38 rear
Gates SA-39
Gates SA-39 rear.  Note replacement power and input transformers

Now that's what I'm talkin' about! Thanks Doug!!!

---Joe

 

[analag]

A lot of money, time and effort. I have enough tubes to re-tube it three times. As much as I love it, I wouldn't build another one...too much work.