G-PULTEC problems, please help!

[audiophreak]

Hi alexc,
         
          Thanks for the pic .    It looks like you have a lot going on there as far as grounding goes.

  First off ... I am NO EXPERT -  so please take care with voltages and I hope the more experienced will chime in  ;D

  from the pic it looks like you have 7 ?  wires going to a " Star Ground "  bolt , then  another wire going to another ground bolt on the side panel by the PT ?  is this correct ?  if it is , that may be one problem - I would scrape the paint off from around the bolt that the 7 wires converge and that becomes the one and only ground point ( assuming I haven't missed anything )

... also , what are the white,red and black wires from the front panel going under the PCBs ? 

  ... another observation , you have 4 relays on the in /out puts for true bypass , and also a " power on " lamp  -  are you powering all of these from the 12v secondary ?  and if yes , what is the amp rating / output of the PT ?    two tube heaters, 4 relays , and indicator lamp may be too much of a load ... possibly

 
  ... ok , that's all I got , please be careful
    and I hope  it all works out for you , please post back with your progress

 

[alexc]

Been there, done that. Was careful. Have done this many times now.
And I measure the effect of each additional grounding activity as I go.

The case pieces don't make good contact, hence the ground wires connecting
the side back and bottom. Otherwise, a good deal more noise. Easier than removing
paint all over the place and also reduces connection resistance over paint removal.

Other wires are relay bypass switched power with bicolor leds, I run them at around 11VDC.

Nope - all the ratings are fine. Coils are 20mA or so each. Leds are about 5mA or so.
Thats around 50mA additional per channel. Which comes off pre heater regulator.

Along with around 400mA or so for a heater, thats around 450mA of transformer heater secondary. per channel with some  2W or so on each heatsink. Those heatsinks are good for 5W or so before getting too hot.

Traffo secondary is 9VAC (no CT) at 2.5A. Plenty there.
HV is 250VAC (no CT) at 100mA. Not even close there.

There is an additional 24VAC (no CT) which I don't use because I measured the noise
contribution of feeding the extras from one main PCB as around 1dBu worse.
Which is just fine.

What I've found is that every situation in different and there is a lot of experimentation
to get the best performance. As I said, the noise floor is now a couple of dB worse than
perfect right now! This puppy is in service - no more work required!

Cheers

 

[audiophreak]

This puppy is in service - no more work required!

Awesome ... I really am in love with how these things sound        that PT seams a good sollution for the 230 mains situation too.   
                                            Congratulations !!!

 

[schrobbelbop]

Now running the dual pultec without any audible hum!

Feed both the 6.3v heaters with only one psu section.

I now bolted 2 heatsinks on 1 lm317, gets verry hot, but works fine. for sure i'm gonna ad a lager heatsink and attach it to the chasis.

left channel is just a tiny but hissing in the top end.. mayby a bad tube

 

[audiophreak]

Now running the dual pultec without any audible hum!

Feed both the 6.3v heaters with only one psu section.

I now bolted 2 heatsinks on 1 lm317, gets verry hot, but works fine. for sure i'm gonna ad a lager heatsink and attach it to the chasis.

left channel is just a tiny but hissing in the top end.. mayby a bad tube

  Good News !!!!  Congratulations !!!    ... how about some pix of the new baby 

 

[schrobbelbop]

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Up next, wiring the bypass pcb and get my HT voltage down it's now at 298... killing my tubes

 

[audiophreak]

AAaahhhh  ....  Franks Enhanced Pultec filter boards with Gyraf SRPP tube stage .... EXCELLENT !!!!

    Looks great !!    Congratulations !!

  I may have some questions for you , as I am 80% done with a Dual unit of these myself  8)

 

[mitsos]

nice, good job. Glad it's as simple asthat. If the regulator heat bothers you you can also stick a series resistor to drop a few volts before the regulator, this way you can split the heat between the two.  I'd still swap the 317 regulator for an LM350, it's the same footprint, and is capable of higher current output at the same In->Out voltage difference, so it will be more stable over time.  Or just take it all out and go passive CRCRC!  8)

 

[schrobbelbop]

2 tubes suck out 0.73 amps, why change the 317 if it can handle 1.5 amps?

 

[mitsos]

2 ECC88's in series will use 730mA, a HUGE load for an LM317 which maxes at 1.5A (ideally with sufficient heatsinking) and 1A diodes. Give your heaters more breathing room.  That's also the case with the power trafo, make sure it's sufficiently spec'ed.

Note the word "ideally."  The datasheet specs are given for the metal can "K"package (TO-3), not the T (TO220) that we mostly use. TO220 is much worse in terms of heat dissipation and thus current limit, I don't know how much, because national doesn't specify.

Looking at it that way, the 1.5A limit doesn't seem a realistic limit, especially considering the heat produced at 730mA.

 

[JW]

Hey folks, I asked about output transformers earlier as far as upgrading from the Edcor I have in there. I'm thinking I will eventually change these pultecs to be closer to the original EQP-1A, so my question is, concerning a couple output options in the meantime. Trying to save myself some trouble in the future.

One is the 9600:600ohm Carnhill VTB2291 that AlexC mentioned earlier http://www.audiomaintenance.com/acatalog/Transformers_and_Inductors.html wired 2:1 or 4:1

The other is Sowter's Pultec output (9530) 7K2:600ohm  http://www.sowter.co.uk/specs/9530.htmbeing

If I got the more expensive Sowters, do you think they would work well after the SRPP stage for the time being? (it'll take me awhile to get around to building the original pultec amp/interstage section etc.)

The Carnhill's are cheaper but I don't know if I'd they'd be as good later if I built an amp modeled after the original EQP 1A, because they don't have the the feedback winding? 

Just thought I'd pick your brains . . .

 

[alexc]

SRPP in the gpultec circuit needs 2:1 otherwise you will have an output less than unity.
The SRPP make up amp is not really able to provide any more gain.

So, not recommended to have a higher ratio step down than that unless you want to use
another gain stage after the gpultec.

The original make up amp is very different to the gpultec so not really able to migrate from
one to the other. Basically it's a complete rebuild of the make up amp to get closer to the original.

Cheers

 

[schrobbelbop]

Up next, wiring the bypass pcb and get my HT voltage down it's now at 298... killing my tubes

Finished! Bypass pcb is working, but had to add 3k3 resistors to my bypass led's because if i switched in bypass the relais didn't work when flipping de switch fast.. so led's are lighting a bit softer.... think there is not enough current.

HT is now 246v with 15K
heater voltage is 6.1v should be no problem i guess?

only thing left is the 6.3v diode rectifier is getting a bit hot... future will tell

 

[Songguy]

I finished my g-pultec but have a problem. The HF controls are not working properly. LF works fine but the HF changes in frequency , boost and cut are barely noticeable.

My voltages are not right.

HT is 324V not 250
6.3V is 6.14V
The 220v coming off the transformer is 259V
The 9v from the transformer is 10.6V

Anyone think I only have a bad transformer? I'm using don-audio g-pultec transformer.

 

[gyraf]

Increase value of resistor between ht-capacitors until you have ca. 250V at tube anode.

This is rather important in order not to burn out tube early.

HF-boost not working can be either wrong or wrongly mounted parts (in particular the inductor), and/or too high a driving impedance (the pultec filter requires being driven from low-z source)

Jakob E.

 

[Songguy]

Hi Jacob,
I still can't figure out what's wrong. Now no audio is passing at all. I checked all the caps, inductors and pots on the filter section and they all appear to be correct and in the correct places. There is continuity between all contacts.

One thing I noticed is that the LM317AT is really hot! if I touch the heatsink with a moist finger it actually makes a sizzle sound.

Do you think that larger resistor you mentioned before and a new LM317 will help the issue?

Chris

 

[who]

Hi Chris, just stumbling trough your thread.
How did you measure the voltage comming from the trafo? Before i send trafos i test it myself to prevent sending the wrong types (i have also a similar trafo in the program for mila projects with 250v) but 259v is too high for this trafo secondary and absolutely not normal... Do you have more detailed pics of the trafo and the connection?

Did you measure the DC voltage with the trafo connected and behind the bridge rectiviers or the disconnected with an measuring tool switched to AC? I ask cause the DC Voltage is >3XXvDC and
The other voltages seems to be ok, there must be a problem only with the hv path. Might be the resistor or the lm317 You might check it again. The LM317gets so hot cause the 259vdc. This is the absolute maximum better you put in a bogger resitor between the two big caps to get it down to min 250vdc (like Jakob sayd). Please disconnect the trafo and measure the AC voltages of the secondarys. its voltage should be 220vAC and not around 259vAC i will send you a second one of course then but honestly i can not beliefe that. I also contacted you via email. Let me know if you have any questions that i can try to help finding a solution.
Sincerely "who"

 

[audiophreak]

Hi All,
        A while back I successfully completed a Dual  G-Pultec with no Hum or Buzz issues with a Hammond PT that has 250vac secondary @140mA  and a 6.3vac secondary @2.0A    I wired the PT secondaries to a terminal strip and then split from there to the two separate PCBs.  The PT housing and IEC Earth connector both secured to a Star Ground Chassis point, but no circuit to Earth / Star ground point.

      I haven't had a problem yet , but this has always bothered me - so what I have done is strip all the PSU components from  one PCB and ran jumpers to get from PCB power inlets to proper traces  , Then on the other PCB ,  lowered the big dropping resistor and ran jumper wires to the other PCB from HT , Heater and Ground, Tapping off the ground wire that goes from one PCB to the other, and connecting it to the Star Ground point. So the circuit is now Star/Earth grounded , and i think by virtue of the XLR cable Shield from XLR connector to PCB - the incoming signal / piece of kit and outgoing signal/ piece of kit are now earth / Star grounded - so no additional wire from XLR input to Star Ground is needed ... right ??   

    I use the 1086 regulator for the heaters and its rated for 1.5a  , so it never gets too hot  -  on the HT side I have 250vac regulated to about 350 , with a 12k5  /  7w dropping resistor the HT goes up to about 310vdc from first fire up for a few seconds , then settles around 220vdc - heaters are at 6.2vdc 

  It all works and sound nice - but wanted to post what I've done ,  and see if anyone has any comments / suggestions  / recommendations 

  Thanks to All 

 

[JW]

Hey guys,
I have a couple Cinemag CMOQ-2S transformers that I had forgotten about. Can these be used as 2:1 output transformers?

It's a four winding transformer.

Cinemag doc says it can be driven by source impedance of up to 600ohm. Is that a problem?
What if I wire the primaries in series and just use one pair of the secondaries? That would make a 2:1 output, but would it be too much of a load for the SRPP stage?

http://www.cinemag.biz/output/CMOQ-2.pdf

If that doesn't work, I can pull a couple OEP262A2E's out of my dual G1176 inputs, as I almost always like the IC input better (I have a switch in there)

Anyway, in regards to wiring a OEP 262A2E as a 2:1 step down can someone confirm that my wiring is correct?

This per Mnats' page, in regards to the G1176. http://mnats.net/1176_revision_j.html
But I think it's how you would wire the OEP for 2:1

The OEP has pins that look like this:

Pri      S1 S2 F1 F2

Gnd pin

Sec.  S1 S2 F1 F2



Pri:
Use F2 for +in, jumper F1 and S2, S1 is 0V from the board, and connected to ground pin

Sec:
F2 is + out, jumper F1 and S2, S1 is -out

 

[nadje]

Hey Guys,

I have finished building my dual pultec eq and am now in the stage of getting rid of hum and unwanted artifacts. One thing that occurs is that when audio goes thru my unit and i actually touch the unit you can hear this fairly good through my headphones. So like if i tap on the front panel. Also i hear i high pitched sound now and than that are the tubes? I think i've made a grounding mistake of some sort. Has anybody had experience with this phenomenon?