G-PULTEC problems, please help!

[missi93]

Here is a Screenshot from a Real Time Analyzation with a 11dBu 1kHz signal going through the G-Pultec

 

[missi93]

and another one , same signal , same level going through the Pulse Techniques.

Some impressive numbers.

Thanks for your time guys,
let me know what you think!

M.

 

[missi93]

Hey again,

I still have one problem. After seeing the tube main voltage at 360V ! I upped the 2W resistor to 5,6k first and then 10k and now it's sitting around 280V. Is it still too high?

Isn't there a end point where it stops making sense to put higher resistors?
Or should I just go higher Ω until I reach the 250V recommended?

M.

 

[gyraf]

That's an awfully high voltage - is your transformer correct type?

But yes, definitely best to be below 250V - that way your tube has a better chance of having a decently long life..

/Jakob E.

 

[missi93]

Yes the values should be right, it is the Mono G-Pultec Transformer from Don' Audio with a 220V secondary.

I don't get why it outputs 300 or more.

I will make another overview soon, and see how much exactly I am getting from the transformer.

M.

 

[Gustav]

Yes the values should be right, it is the Mono G-Pultec Transformer from Don' Audio with a 220V secondary.

I don't get why it outputs 300 or more.

I will make another overview soon, and see how much exactly I am getting from the transformer.

M.

220VAC rectified = about 305VDC

Measure the AC off the trafo before connecting to the circuit - might give you a clue.

Gustav

 

[Whoops]

I'm cleaning my workshop and found 2x G-Pultec pcb sets
I put the set for sale in the black market in case someone is interested:

https://groupdiy.com/index.php?topic=76070.0

 

[innercityman]

Hi guys,

I'd like to built a stereo unit in one case and I'd like that only one knob, pot, switch, controls both sides... Do you think it's possible to do that ? How difficult would it be ? Does every component from one side to the other has to be matched ?

 

[innercityman]

Ok, maybe stupid question. Anyway...

Could it be as simple as using 2 G-Pultec PCB kits and using dual gang potentiometers and dual gang rotary switches to control both channels with knob ?

 

[gyraf]

Yes, you could do that - but you'd need to select your tubes, inductors, capacitors and possibly resistors in order to get decent tracking between channels. These mentioned in order of importance.

Specially the high-boost inductors AND capacitors used there need very high precision in order to not get annoying at high Q's (for my G14 I aim for 0.3% on both inductor and capacitor).

Note, on the other hand, that the absolute values are not all that important, so you can just buy a big handful of parts and match from there..

/Jakob E.

 

[Whoops]

Could it be as simple as using 2 G-Pultec PCB kits and using dual gang potentiometers

[/quote]

You could use Dual Gand Pots, but be aware that potentiometers have a tolerance of 15% to 35% (more or less) depending on brand and type, that tolerance will also apply to individual tapers inside a dual pot. So A dual 50K pot, can have one gang at 47K and the other at 52K, having the different values in the middle point.

Or you are able to get Dual Gang pots with tighter tolerances, probably more expensive, or you buy a lot of them and measure to select the ones were the gangs are closer in value.
Or you replace the Pots with Dual Gang Switches and use 1% metal film resistors

 

[innercityman]

Very interesting informations...

Or you replace the Pots with Dual Gang Switches and use 1% metal film resistors

That would be a too much expensive option I guess.

Note, on the other hand, that the absolute values are not all that important, so you can just buy a big handful of parts and match from there..

That seems the better option and probably my choice.

I still have a question... Does the components quality especially caps, has an influence on audio quality of this design ? I mean, buying expensive caps like Mundorf supreme line or so worths it or not ?

 

[gyraf]

Hifi bs definitely not worth it. Go with decent quality, e.g. Wima...

 

[Whoops]

That would be a too much expensive option I guess.

So good luck in trying to match 20% tolerance Pots, or even 10%.

You can build at least a really nice "Unmatched" Stereo Pair

;D ;D

 

[innercityman]

So good luck in trying to match 20% tolerance Pots, or even 10%.

You can build at least a really nice "Unmatched" Stereo Pair

Ok Whoops, I don't want to build a mastering unit, but at least one, or a pair that I could use inserted on a mix buss. So Maybe I'll forget this idea of one set of knobs to control both sides and go to the more classic way of building two channels in one case but with two sets of knobs and try to use the closer in value pots.

It will be my third Gyraf project, after the G-SSL 4000 like every newbie I guess, and a G9. Thanks to Jakob for offering such great projects to the DIY community. I love my two other units. I added some options on my SSL like, turbo mod, Crush N' Blend and a pair of Lundahl LL5402 output transformers, and I just love it. I use it on every mix.

The G-Pultec original design has low frequencies that I'd like to change and go with the Original Pultec ones... 20, 30, 40, 60, 100 (90), 120... Do you know which capacitor values I should use to obtain those frequencies ?

 

[Bij]

Hi everyone, and many thanks for all the precious informations.
I sorted a few issues with my dual Gpultec, I had a faulty power transformer with no 25OV output.
I replaced it with one that have three secondaries : 250V/0.1A, 6.3V/1.5A, 12.6V/1A

I have 274V AC on the HT, put a 33K/1W B+ adjust resistor and get around 190V DC on the plates.

The two LM317 are fed with the 12.6V output. Everything was testing fine for a short amount of time, but one of the LM317 blew away.
Maybe too much heat dissipation did that, they are both dissipating through the chassis.

Now my question is : Since I have a 6.3V secondary, could I use it, bypass the LM317 circuitry and get heater voltage directly after the 4700uF filter cap ?

 

[gyraf]

if you have a 6.3V secondary, you can AC feed the heaters - these are.. .. .. 6.3V

However, you can't rectify your AC to DC, that would give you 6.3xsqrt2 = 6.3x1.41 = 8.88V DC (vhich is obviously too high)

317's very rarely blow - they are safe-operating-area protected. It probably had a short to the HT voltage, these sorts of overvoltage issues are the only things that reliably destroy 317's


I'd just try again. Or as mentioned, go with 6.3V AC directly to tube heaters

/Jakob E.

 

[Bij]

Thank you Jakob,
I assumed I could add a resistor to adjust the voltage.
Anyway, I get your point, a new LM317 is on its way.

 

[TillM]

I've a strange problem since two weeks.
The unit works nice without any issues, but now this happens.
When the unit is one, for lets say 1 hour, it makes a high frequency noice (i would say at 11k/12k) in the signal chain.
Not loud but noticeable.
I don't have change the tubes, cause I have no ecc88 at home.
But for me it's not a typical tube defect.
What could be the problem.
As I said, the unit works great for a year.

 

[rock soderstrom]

I've a strange problem since two weeks.
The unit works nice without any issues, but now this happens.
When the unit is one, for lets say 1 hour, it makes a high frequency noice (i would say at 11k/12k) in the signal chain.
Not loud but noticeable.
I don't have change the tubes, cause I have no ecc88 at home.
But for me it's not a typical tube defect.
What could be the problem.
As I said, the unit works great for a year.

Defective tube due to exceeded max Ufk? Is the filament elevated? ECC88 can only withstand 120-150V depending on the manufacturer! This can lead to whistling tubes...check the upper Triode in the SRPP for this.

Osicilation because of capacitive crosstalk?