Pultec output sounds too quiet

Hey guys,

I have almost finished my Pultec PEQ1A EQ (SRPP-based version), well at least the inside, and everything seems to work according to plan, all for the fact that the output volume is very low. Could this be, because I used an old (and used) Amperex ECC88 'Buggle Boy' tube (I thought that would be a nice tube for the Pultec)? Or shouldn't the tube, used or not, make any difference in the output volume? Advice appreciated, thanks in advance!


All the best, David.

Start with the power supply first.
Verify B+ volts at 250-275.

Next, make sure the voltage is reaching the plates by measuring the plattes of the tube sections, pins 1 and 6.

Check bias voltage on cathodes, pins 3 and 9.

Tube is lit up, right?

Next, bypass line amp and set all eq controls to off or flat. See if output at end of passive filter is equal to input minus a few ac milli volts.

Next, see if output voltage is reaching the pri of the output transformer.

What kind of transfomers are you using?

If transformer is being fed healthy ac signal but output is low, check pinouts on transformer.

Report findings at your convience and have a nice weekend.

Hi CJ,

Thank you very much for your answer. I will check the things you mentioned today and I will post my findings soon. By the way, I am using Lundahl 5402 (2 times). Have a nice weekend!


All the best, David.

Hi CJ,

Thanks for the useful tips,
thanks to you I've managed to fixed it.

Solution : take a 3~4 A fuse for the fuseholder on the PCB.

Cause :
It turns out that there is a small difference between the original design and the PCB I've received.
The fuse on the PCB is not the fuse in the schematic.
The PCB does have no fuse holder for the first transformer (220v -> 12V), this fuse should be added in a normal external fuse holder (like you normally see on the back of equipment).
The fuse on the PCB is an extra security measure for the second transformer (12V -> 220V) and should be around the same amperage as the transformer (3.3A in my case).

When the Pultec powers on the capacitors in the tube section (2x 220uF-350V) draw quite some current, and a 315 mA fuse is far from sufficient. In my case a 4A fuse worked fine.
Initially there was no 250V on the socket of the tube.
After using a more powerfull fuse, it measured around 290V (probably because there was no load of the tube.

I hope this describtion may help out someone else facing the same problem.


Be carefull when measuring when the power is on.
220V might potentially kill you.

For the good order: the above message was written by a friend of mine (under my Forum name) who is helping me build the Pultec and a 1176. He has a whole lot more electro-technical knowledge and experience than me. Again thank you for the tips CJ.

excellant!

[quote author="CJ"]excellant![/quote]

Hi CJ,

Just caught your MPS-note in another thread - PMd you

Bye,

Peter