[BUILD] GIX-51X tube preamp

[gemini86]

V2 is looking much better,

V1 still is a concern.

Check R6,7,8,9. Voltage across R6 should not be 39 volts. Try to measure the voltage across R6 directly.

 

[Benny]

I checked R6,7,8,9. Their values are o.k. Voltage across R6 is 0.9mV.

 

[gemini86]

Hmmm... not sure what is happening. Power off, pull the tube and measure continuity between pin 7 and 8.

 

[Benny]

Continuity between pin 7 and 8 with both tubes taken out:

V1 - 0.996MOhms
V2 - 1.498kOhms

 

[gemini86]

Well... that seems okay.

Your input stage biasing is off, but without good pics of the board and related components, I can't tell why.

If you've double checked resistors, checked for solder bridges/shorts between pins or other pads, then try injecting a signal and measure the level at the different stages. Start with a 100mV sine, 1KHz, right into the instrument jack. Turn the gain all the way down, output pot all the way up. Check AC signal voltage at each stage.

Also, post pics if possible.

 

[Toure14]

Hey Rodney I have a quick question. My C506 Capacitor is small so it fit right in the small lead spacing but looking at it I see neither leg toches the trace is this a problem?

 

[Toure14]

Again the cap I used doesn't touch the trace. A pic from the bottom view of C506

 

[Benny]

Hey Rodney I have a quick question. My C506 Capacitor is small so it fit right in the small lead spacing but looking at it I see neither leg toches the trace is this a problem?

Hi,

you should put C506 in the two holes with the wider lead spacing. There are different lead spacings for different sizes/brands of caps. The way you've put it in, both pins are connected together.

 

[gemini86]

Benny, you're correct. The you have it now, toure, the cap is just soldered to both ground pads.

Are you sure that cap is a 100nF/250V? It looks ceramic, which is fine, but just looks a little small.

 

[Toure14]

Yes it is polyester film but I already cut the leads so off to radio shack I go

 

[Toure14]

Rodney is it ok to clean the boards with alcohol after everything is soldered on?

 

[gemini86]

That's what I usually do. I prefer to use 99% alcohol, rather than the 70% that some stores carry for medical use. It's probably very clean but the water content may cause some residue/noise in high impedance areas.

 

[Benny]

Well... that seems okay.

Your input stage biasing is off, but without good pics of the board and related components, I can't tell why.

If you've double checked resistors, checked for solder bridges/shorts between pins or other pads, then try injecting a signal and measure the level at the different stages. Start with a 100mV sine, 1KHz, right into the instrument jack. Turn the gain all the way down, output pot all the way up. Check AC signal voltage at each stage.

Also, post pics if possible.

I checked all resistors twice, today and they all seem o.k. I'll post some pics later today.

 

[Toure14]

Almost Done with my Black face and my White face I have a question. In the instructions it left out the "FIL" pads do I just solder some wire to those pads? or I do not need them?

 

[gemini86]

Yes, connect the filament pads. Any two conductor wire will work, I used a pair of solid 18ga twisted together.

 

[Toure14]

Who sells the OEP transformers in USA?

 

[gemini86]

Newark.

 

[Toure14]

Rodney I'm gonna shoot you a pm...but for now I'll ask another question. Seeing as how this pre has no lighting indication is there a test procedure to make sure everything is working upon initial startup?

 

[tonycamp]

Hi Rodney, i've been mia on this thread for a bit, been cutting my teeth on a lot of projects possessing lower voltages ;D love the way everyones been contributing to smoothing the bumps out of this unique 500 tube pre project! I should be starting my pair soon, but mostly wanted to chime in to say congrats on being a new Dad!

T

 

[gemini86]

Haha, thanks tony!