the Poor Man 660 support thread

[MartyMart]

REQUEST :

Would any of you kind fellows happen to have ordered extra parts than needed for a PM670 ?

I have most things ( have been going through projects to see whats missing, had 4 years off!! )

Here's the few bits I am short of :

IRF840's
4,700uf caps
1000uf caps
Diodes/Zener ( apart from 4007's )

Thanks
Marty.

 

[MartyMart]

After reading through what seems like a "War and Peace" sized amount of text, I have done the following:

Ordered a "one off" transformer with increased spec for the 9v heater rail of 10A & shielded ( expensive but better than having 2 x)

Ordered 20 x 6N5P Russian Mil spec tubes and all 1% resistors, perhaps help in channel matching, though I am really
thinking of this as 2 x 660's in a box.
Will build LoLo's tube matcher circuit.

It's not the first priority but when I do it, it will be "right" !

Marty. ;D

 

[alexc]

Another brave soul! To boldly stomp where few have gone before 

I do think the 6N5P sound good here and I did find better matches than 6BC8.

With your titanic heater spec you should be  .. fine!

I have one channel that way now and a dual-channel with the 6BC8.
The 6N5P has more GR and more gain before getting too crunchy.
So that would be my choice for a cleaner unit with less need for gain at the desk - these guys can strain a little with level.

Sounds like you are ready to put some time into the build - the psu seems to cause people issues, so extra care there is a good idea.

Not sure of your planned traffo placement, but if possible, be flexible with placement till the end.

I started with the straight 4 on the floor layout and tossed it out as soon as I got to serious testing.
Big performance gains if you can find the furthest away and best orientation.

Of course, that's not always possible and may *look* like crap.
But it can be worthwhile and the difference between really hum free sound and so-so noise levels.

Hope you make it to the small club of successful PM670 builders and even more exclusive set of those happy with the result!

Cheers

 

[MartyMart]

Thanks Alex, I am watching your "pimped" P2P version thread with interest, sounds like you are
almost there ?
My tube experience is fairly "low brow" but I have built 2 x tube Guitar amps on "turret board" and
also a successful DAOC - which just needs better I/O traffo's and the bypass circuit installing ( who needs bypass? )

Good to have all that knowledge and info posted to read about, do you think some kind of "slow start"
board would be beneficial, or even just a Tag board / P2P version of the power supply board ?
I can't quite remember if that was the cause of "some" problems or just a bit fiddly to deal with "IF" a
problem arose from a builders mistake ??

Cheers,
Marty.

 

[alexc]

I would avoid complicating things with a slow start reg heater or a scamp type addon - just my 2c.

PS - there is a bit of a trick in using the off-board time constants network ('blue bird' network) as well as retaining the on-board large timing cap. It's worth doing if you have already installed  that big, expensive 10uF wima and don't want it unused.

Basically a trace cut at the connector which goes to the 'attack' pot on the original schematic.
If you want to know more, let me know.

This is actually a fairly simple build conceptually - careful assembly and wiring I think is the main thing.
If you can do turret in a guitar amp you can do this for sure.


>  ( who needs bypass? )

I do! i can't imagine not having it.

The PSU pcb is not that bad - just take some care and you should be fine.
Solder bridges, bad solders, wrong component orientation - the usual suspects.
Mount the higher power resistors a bit higher off the pcb. Mount the transistors not all the way down to the pcb.
Check your heatsink is properly insulated and not at hv.

If you blow the HV sections once, repair and incorporate the mods posted earlier.
A couple of protection diodes. It can help get the whole thing working for you.
I did only when 1 blew once   on one pcb. Not on 3 others. All 4 worked first time.
One blew because I was dicking about with it! Like shorted the HV while fartsing about with stuff. Big bang! (bang)
Other people have VERY strong opnions on the matter.

If anything, maybe get yourself a spare pcb in case.
As for reworking the psu pcb  altogether - maybe that is good for you. Not something I would do.

In a dual unit, there isn't much room - it's the reason the psu pcb is 'compact' in the first place.
Trying to 'better' it in the same space would take more effort than making one work and having a spare.
At least that's how I see it.

And thanks for the 'pimped p2p' noticing - I got me some mighty troubles right now.

But I WILL prevail

 

[MartyMart]

Alex,
Would like to know more re: bluebird wiring, though boards are empty so far and i DO have those
expensive MKP 10uf's !!

I have 2 x sets of boards, so if something does go wrong, I can start again but I would prefer to get it
right first time.
How difficult is the extra diode protection mod ... worth doing from the get go ?

I was thinking to put the small TO92 sized stuff on sockets, save de-solder etc if there is an issue.
Any reason that the IRF840's ( which I don't have ... got any? ) cannot go insulated and "off board"
to the case side ? .. would make access a little easier without those heat sink "mountains" !

I will take your advice and leave out the slow start / SCAB boards, I can see the space being a problem.

Sorry for the questions but it really helps and is much appreciated

Good luck with your problem solving ... YOU can do it !
Marty.

 

[alexc]

I'll do a description of the keeping the 10uF timing cap + bluebird options mod I did shortly.

Basically, the idea is to replace the single, 10uF cap with a parallel, switchable network of varying caps+resistor branches, replacing the 'attack' pot altogether.

It's easy to do by removing the big 10uF cap and putting wires in it's place to the off-board rotary switch.
That switch has the different branches, one of which is selected and put in circuit, in place of the 10uF.

To keep the 10uF on board, and not have to transfer it's big *** to the off-board rotary switch, you need simply to break it's 'positive' terminal and send that to the rotary as one of the parallel branches.

The 'negative' terminal of the 10uF is common to all the branches so nothing needed there.

In the end, it turns out to be a simple cut and jump near the attack connector.

Otherwise you need to remove the 10uF, replace with a link and it's gone! Which is a drag if you just spent $15 on it!
At least to be reproduced at the switch, which is also a drag.

Get my drift?

 

[alexc]

I should say that 10uF release timing is very, very long. So for new players I would say don't spend it. Jumper it.
4uF is the absolute max I have actually used.  And not so often!

I just hated to toss it, so I kept the original. My most common used is more like 1uF or so for the release
(in parallel with the existing, hard wired cap+resistor network of 221K//220nF+120R)

Anyway - you need to review the 'bluebird' mods - those were (amongst) the earliest timing mods I recall.

Cheers

 

[MartyMart]

Sounds good, perhaps I can "forego" the HUGE 10uf's and place the various other cap/R options in it's place !
There would be enough room in it's "spot"

I have everything from 2U2 down, so perhaps that would be fine, I never use release over 800ms anyway.

Cheers,

Marty.

 

[DerEber]

I did use some other timing RC combination, but still implemented the 10uF for the like auto-mode. One with a even bigger R in series with the 10uF. It´s a good place to play around.

 

[MartyMart]

Check my PM670 transformer out here :
http://www.groupdiy.com/index.php?topic=52571.0

Mighty and powerful !!

MM.

 

[duantro]

That ought to get the job done! I took a similar route and got an 11amp heater toroid ( only thing I could find above 6amps), after reading all of the horror stories here!

 

[MartyMart]

That ought to get the job done! I took a similar route and got an 11amp heater toroid ( only thing I could find above 6amps), after reading all of the horror stories here!

Cool, I figured 10 A should just about do it !!

It will have to go on the side of the case, just hope the rack doesn't buckle under the weight !!

 

[duantro]

I finally had a chance to search out my problem.  I found another dead input transformer lead. Man that's the fourth one! I'm goin to save some money and get 4 input cinemag cmli-10/600, or 4 lundahl's like Kingston used. Or possibly get the Sowter 4383?

 

[alexc]

Bummer - I had this with the specified edc traffos too. Using up the last xsm now, never again.

However, even with the 4 or so edc xsm I had to toss, it still came out less $ than the premium stuff and has been in service for a few years now.

Good luck and persevere. There was never a vari-gm diy without  catharsis before the end. And sometimes even, bitter tears.

 

[duantro]

Replacement Edcor transformer showed up and I had a minute to mess with this beast.

Intermittent channel works great now with working transformer.
I also got my meters to zero out. I used 1k trimmers that were almost shut all of the way off, with a 3k9 on + side like Tekno808 posted a ways back. Now I can drill holes in panel to put trimmers.
I'm going to consider the lowpass sidechain mod Kingston posted. While I'm drilling holes, might as well put toggles for this mod while I'm drilling.
I have different switches for my time constants that I will change out also. I had the wrong degree spacing engraved on my panel.

 

[duantro]

Meter adjustment trimmer hole drilled and trimmer mounted.
I did some experimenting with my time constant switches and must have screwed something else up, or perhaps the travel to my studio shook something loose. ??? I'm now getting a random motor boating sound on my left channel (not the one with the bad transformer previously), when driven a little, and also have fluctuating voltage on r10 (~10V-13V) when the threshold switch is increased. I've read back and found that KHStudio had problems with output tubes causing these symptoms. I'll try to swap these tubes out and see if it is the problem.

 

[alexc]

You might also check your heater supply - just a look to make sure the ripple is what you expect it to be. I've only done that with a CRO.

I've not found the hv supply on these to give any trouble in terms of noise of various types - when they go they're pretty right.

Given there's not much else in the signal amp, motoring noise is likely to be a GR tube (I've had it) or heater (I've had it) then maybe some wiring in bad shape (sure been there : ); generally the traffo-pcb or atten-pcb wires.

(not much else is there : )

I've also had the trimmers go bad once - I think this is primarily because I used 'cheapo' types here and I was messing about  for a long while. If you can adust to a steady dc on those, and it mostly stays there, then thats fine.

From memory, cross talk of control amp into signal amp was not an issue either.

Then of course, there's the bottom  line noise floor.
Postitioning of stuff, including wiring, is paramoun in looking for best you can achieve.

After all that is sorted, you can then give some mind to time constants and so on.

--

R10, the cathode common resistor should be prettty steady for dc. It can move around some with signal but dc should be relatively stable.

If it's not, then would be a tube not right or your 'thresh' switch wiring, either a basic bad connection thing or worse, a balancing thing (not put together right). And after that, a transformer thing  ???

 

[duantro]

I swapped out tubes, and it is still happening. I also switched out time constant switches, and it still happens on the left channel. My voltages at the check points are all pretty much dead on.
I did notice that compression goes from not working on this channel's meter, to working with the motor boat/ shorting out sound. So it appears that I have a bad connection/ short somewhere.
.......Perhaps I'll have more time soon to search more and find the culprit.

Update: When i switched the threshold switchs, i had 2 wires, on the top deck, in the wrong spot. I was relieved when I found it, no more motorboating, but I'm still getting some distortion. ???
I've swapped channels with my scamp board ( problem exists in scamp and analag mode, however it is much more drastic with scamp in fast setting) I've also reflowed solder on main pcb and the problem still exists. It sounds like a clipping distortion on the attack of program material, and fuzzy on test tones.
I will try to swap transformers around next and maybe re check tube matching?

 

[duantro]

So......While taking time away from this, I finished my PMEQP1A/5 from Ruffrecords, which sounds sweet!
In the meantime, I ordered 4 Cinemag CMLI 10/600 transformers to try out Kingston's M670 mods. I swapped out the input on one side, as well as put a 600 ohm t-pad before the Cinemag input, and..... viola!!! No more distortion/ clipping on that channel. I had tried swapping the gain switches previously, to make sure I didn't screw up somewhere, and it  still happened. So that totals 5 dead edcore's. Those things must have had a bad travel experience.
So glad to have found this.
Edit: Holy crap these Cinemag transformers sound so good!
Edit 2: I'm going to implement most of Kingston's m670 mods, since I have switched over to non center tapped input transformers, so I'll be posting over there from here on out. Thanks for the help AlexC and others!
http://www.groupdiy.com/index.php?topic=51478.100