Avalon vt-737sp

[Jdm5149]

Regarding the readings. Would no voltage at T10 be problem ??

 

[orpheusmaximo]

Hi folks. I have a great working blue led 737
With Telefunken tubes BUT for the bass section in the eq?

Both knobs, volume and low-eq. no
sound

I tried the internal blue trim-pot, no sound.

Any ideas? Thanks.

 

[pucho812]

Hi folks. I have a great working blue led 737
With Telefunken tubes BUT for the bass section in the eq?

Both knobs, volume and low-eq. no
sound

I tried the internal blue trim-pot, no sound.

Any ideas? Thanks.

The Trim pot is specifically to make the eq flat when the pots are at center detent and the eq is kicked in.
So if I did a sweep with the audio precision there would be a line at fixed sweep level with no bumps or dips.
Your fault will be in a couple of possible spots, the main board where all the daughter boards come off of or the eq daughter board, the long rectangular board behind the eq pots. That is assuming the eq pots test ok.
Start there.

 

[TheseGoToEleven]

Regarding the readings. Would no voltage at T10 be problem ??

T10 should be +12V DC when the "high gain" button is pushed in, and 0V otherwise.

 

[Jdm5149]

K thanks will test later but probably good. I guess the search continues. Is the 6.36v good for the heaters T2

 

[TheseGoToEleven]

4dbu at 1k. Pad 13 : 1.030v. Pad14 : 5.28v. T9 : 1.030v T10 : .003v. Also T8 : 8.44v. T11 : 1.512v. T12 : 8.56v.

+4dBu is way too much signal for a mic. I would say use maybe a 25mV signal, which is something like 50x smaller! Use +4dBu only when testing the line input.

Anyway this proves that mic signal makes it through the input transformer, out of the gain pot, and out of stage 1 amplification (tube #1).

Edit: Audio signal is also making it into and out of stage 2 amplification (tube #2). But turn that input signal down to get more realistic readings.

 

[Jdm5149]

K. Where would I check next. Is there a place on the i/o board. Or next spot would be tubes ?? I put new set in. All lighting up.

 

[pucho812]

For mic level testing, generate a 1k signal at -20dBu or up to -30dBu
Which in the daw if -18dBFS is +4dBu, -22dBFS would be 0dBu and -42dBFS would be about -20dBu.

 

[Jdm5149]

K. By prior testing can I assume signal goes past those points. Past the area where GoesToEleven suggested

 

[TheseGoToEleven]

K. By prior testing can I assume signal goes past those points. Past the area where GoesToEleven suggested

Next, with a reasonable mic input level like what Pucho suggested, make sure the "compressor", "equalizer" and "meter" buttons are out (unlit). This greatly simplifies the rest of the audio path. See whether you get signal at solder pads 64 & 65 (which connect to the output knob). If there is signal there, then you should also be seeing something on the VU meter.

 

[Jdm5149]

K will do. Thanks again

 

[TheseGoToEleven]

I'm making notes about some of the selected solder points and relays. Could you tell me how the relay underneath the input knob is labeled? It's the one closest to the front panel in the group of 3 relays there (the other two are labeled K5 & K6.)

 

[Jdm5149]

It’s labeled k4

 

[Jdm5149]

K still a newbie. lol. I have my generator pushing out 1k at -22dbu. I have it plugged into mic input and preamp at 12 o clock. Now can I test with a meter at those points again. 13,14,T9,T10. Is that ac voltage ?? T10 I get 12v dc when high gain engaged

 

[pucho812]

Is your meter showing you anything?
Was it passing signal in line?
Sorry if you answered that already but I lost track in the thread

 

[Jdm5149]

Should I be looking for ac voltage At those points. 13,14,T9,62,63,64

 

[Jdm5149]

At T9 I get .069v ac. I have it plugged into mic input and when I switch to line on front panel I have same voltage. No voltage when switched to instrument

 

[Jdm5149]

K. Last test for today. Gonna buy some lead for my scope. Generator pushing 1k at -22bdu. Plugged into mic input. T9 : .069v. Pad13 : .069v. Pad14 : .257v. Pad62 : .005v. Pad63 : .218v. Pad64 : .737v. Haha. 737

 

[TheseGoToEleven]

K. Last test for today. Gonna buy some lead for my scope. Generator pushing 1k at -22bdu. Plugged into mic input. T9 : .069v. Pad13 : .069v. Pad14 : .257v. Pad62 : .005v. Pad63 : .218v. Pad64 : .737v. Haha. 737

That looks like progress to me. -22dBu mic input and approx +4dBu exiting the output knob (pad 63). See anything on the meter?

Edit: Sorry that's not +4dBu on pad 63 but it hasn't gone through the output tube stage yet.

 

[Jdm5149]

The meter sits below zero. When I press it in it pins to the right. Definitely no signal on meter and when running into my console nothing. I stated before that the vu adjustment is pushed down alittle from the work they did on it. They replaced some pots and put regular pots. They put some black stuff to protect board. It’s just something I have to fix later on or might order 2 to do while I troubleshoot