gyraf pultec build in the 110v (us) and transformer heat

[W DeMarco]

So I finally figured out what was wrong with my passive. 2nd trans was shot. I think the pic on page 2 of this thread is wrong. Its the zeeusa post. On the 2nd transformer primaries. Isnt that supposed to have black and red tied together?

On another note I am measuring 290 volts on the resistor after the power caps. Is this bad?

And a final note. When I look at pins 2 and 3 output xlr on my scope one is dramatically smaller than the other. I noted the same on the input however they were opposite. Pin 2 was big on input where pin 3 had the bigger signal on the output. Is this normal?

W

 

[W DeMarco]

I brought the Passive into the studio yesterday and gave it a go. Sounds awesome. Love it though Im still concerned about the 290 volt reading.

Will

 

[gyraf]

Yes. Use some resistors in series with the 3K3 until you get some 250V for the HT at the tube. My guess is an additional 6K8 or so - maybe even 10K.

Make sure that you've completely discharged the electrolytics before touching anything!!!!

While you're at it, it will probably be a good idea to mount a 220K-470K bleeder resistor across each HT electrolytic, in order to get predictable discharge when powered off. Just solder them directly to the copper side of the PCB.

The circuit as-is does not necessarily discharge itself - so check and re-check for safety!!!


Jakob E.

 

[keefaz]

Hi, I have a question :
Is it necessary to put one bleeder resistor across each HT electrolyt
capacitor legs ?

On mine I soldered just one resistor across the legs of one of those caps
and both caps discharge themselves in about 10 min when I power off the
g-pultec.
(when I was testing without the bleeder resistor, the capacitors took more
than 3 hours to dicharge!)

I checked the voltage twice, they are both discharged, so is it a safety rule to
put one bleeder for each HT electrolyt capacitor ?

 

[W DeMarco]

So I am assuming I follow the same procedure to drain these caps as I would use in a tube Guitar amp. Jump the positive lead on the big power electros to the grounded chasis? Im sure I should leave the unit plugged in but turned off to do so. When I drain my guitar amps I have a resistor tied in as well, actually I soldered a resistor into the middle of a test lead I use to drain my amps.

Question two. I just want to make sure my lingo is up to date and theres not a semantical error that we'll have to blame my death on:

On the bottom side of the circuit board I am to mount a 220K-470K Resistor across both the positive and negative legs of the same power caps that I discharged above.

I know about this discharge thing and how important it is but I have to say after seeing Jacob use that impressive large and bold font in his post above I'm a bit nervous about the process.

Is it wise to also connect my DMM to the said 3K3 resistor and watch the voltage fall?

And finally I am wondering about how I am to short these caps after discharging them. Just connect + to -?

Thanks guys.

 

[gyraf]

On the bottom side of the circuit board I am to mount a 220K-470K Resistor across both the positive and negative legs of the same power caps that I discharged above.

If you mean a resistor from plus to minus on each of the two HT electrolytic capacitors, then yes.

Is it wise to also connect my DMM to the said 3K3 resistor and watch the voltage fall?

Yes, always do this when working with high'ish DC voltages. Seeing the voltmeter counting down assures you against a meter malfunction. Measure between the 3K3 resistor and ground - i.e. 0V on in- and outputs.

And finally I am wondering about how I am to short these caps after discharging them. Just connect + to -?

Yes - if you're sure they should be discharged, simply short electrolytic plus to minus with a screwdriver or such. If you see a large spark, just be happy - because it might have saved your life...

Jakob E.

 

[peterc]

Here is an elegant solution to discharging valve amp caps:

http://1176neve.tripod.com/id29.html

Should save on a few pairs of underpants...

Peter

 

[W DeMarco]

Thanks for all the info guys. I have this discharge thing figured now. I used a 200-240 volt light that I attached from power cap + to ground. This light took the stored power down to 150 volts from 250 or so. I then used a second light 100 volts to drain more and finally a resistor soldered in line with test clips to drain the final 60 volts. Works like a charm!! Didnt get zapped once.

On the power rail for the tube. I was reading 290 volts after the 3k3 resistor. Gyraf had me build up the value on this resistor to tame the voltage to 250. Initially I replacd the 3k3 with a 10k which took it down to 265. I then put the 3k3 back in series to make a 13k3 value which landed my voltage to 250 on the dot!!!

Now to build the second one!!

I did notice that my heater voltage was a bit low at 6.12 volts instead of the 6.3 thats called for. Idon't think its a problem but let me know if someone else does think this is a prob!!
Cheers guys!!

 

[gyraf]

I did notice that my heater voltage was a bit low at 6.12 volts instead of the 6.3 thats called for. Idon't think its a problem but let me know if someone else does think this is a prob!!

Heater specs for ECC88/6DJ8 is 6.3V +/-10% - you do the math..

Jakob E.

 

[W DeMarco]

although decimals aren't my thing I'm pretty sure that some where araoud 5.75 Volts is the low side for the heater. Looks like im alright. Time to record!!!


Will

 

[kazper]

If I was trying to have 2 units from one transformer.... and looking at the transformer that is specked out for the Drip opto LA2A clone.. would this work?

Does the 6K49VG work for the circuit? I'm thinking it has the juice to do the job but I'm not sure if the 460VCT means 460 Volts to the center tap or across the 2 wires... I'm a little lost there without having one in my hand.

http://www.alliedelec.com/Search/SearchResults.asp?N=0&Ntt=6K49VG&Ntk=Primary&i=0&sid=45F498001FC5617F

The tube says it needs 0.4 Amp for the heater and it looks like 15ma for the rest of the tube so spec wise this one looks like it can cut it just unsure of the 460VCT.

 

[Siegfried Meier]

Ok, can anyone confirm this. I originally bought the Amveco 62062 and the Triad from the first listed BOM, but am taking them back for a pair of Amveco 62082 for the G Pultec units, as it seems those are the proper ones to use. Correct?

Or, can I keep my 62062 and just buy a second 62082?

Thanks,
Sig

 

[Paul B]

Hi Sig,

I just built mine with 2 62062's and it sounds great, so you could save a few bucks by just getting one more 62062.

The Triad should work, tho, should it not??

Maybe that BOM should be updated, there are also a couple of electrolytics on there that are not on the schematic.

 

[Siegfried Meier]

Great. I'll just send the triad back and get a 2nd 62062. The Triad should work for sure, but I understand it might get too hot. The 2nd Amveco is also a lot neater to install.

Thanks for the info!
Sig

 

[bigswole]

I am about to build the gpultec, this will be my first tube project so i am worried about the high voltage, but.

Here is an elegant solution to discharging valve amp caps:

http://1176neve.tripod.com/id29.html

Should save on a few pairs of underpants...

Peter

Could I leave this connected and use it as a power indicator?

 

[buschfsu]

im having strage voltage readings coming off of my amvecos. can someone confirm how these are set up on the board? i cant figure out where the yellow/red green/purple etc wires are attached to the board.
thanks

 

[W DeMarco]

Busch

Look on page 2 of this thread 3nd post down. Its just below the big diagram of the tranny hookup. A good post describing the hookup. Its a longer post made by underthebigtree. If you refered to the zee1 post preceeding it there is a mistake in the diagram. The primary of the second tranx should be in series. To get it into series tie the red and black of the primary together then shrinkwrap them. Then use the outer two wires(yellow and violet) to the board 220 volt.

BTW what are the voltages your getting?

 

[migidee]

I was thinking of ordering a Triad VPT12-4170 from mouser.  I am pretty sure that its up to spec for the job, and its cheaper than the 62082/62062, but I was curious if any of the more experienced DIY'ers could tell me if it would be a down grade in quality.  It says in the datasheet that there is low straw flux.