Ampeg SVT-6 Pro No Output

[nevetslab]

You've previously established the Preamp works. So I assume we can leave it alone. You've been working on the Power Amp assembly. From the system side of things, your path is Thru the Vacuum Tube front end to the two halves of the Bridged Pair Power Amp. Do either of the halves work....does it pass signal to full output swing, where it clips? What happens when you follow the notes on the schematic? Input level is given. Levels that follow are based on that, given in V p-p to be read on your scope. Are you getting these levels? If not, why not.?

[ca7922303]

You've previously established the Preamp works. So I assume we can leave it alone. You've been working on the Power Amp assembly. From the system side of things, your path is Thru the Vacuum Tube front end to the two halves of the Bridged Pair Power Amp. Do either of the halves work....does it pass signal to full output swing, where it clips? What happens when you follow the notes on the schematic? Input level is given. Levels that follow are based on that, given in V p-p to be read on your scope. Are you getting these levels? If not, why not.?

I will check on what you've told me shortly. I have noticed with gain and master volume turned up past 2:00, the clip light comes on.

[ca7922303]

You've previously established the Preamp works. So I assume we can leave it alone. You've been working on the Power Amp assembly. From the system side of things, your path is Thru the Vacuum Tube front end to the two halves of the Bridged Pair Power Amp. Do either of the halves work....does it pass signal to full output swing, where it clips? What happens when you follow the notes on the schematic? Input level is given. Levels that follow are based on that, given in V p-p to be read on your scope. Are you getting these levels? If not, why not.?

Test points per schematic. Showing both ends on some.

[ca7922303]

Test points per schematic. Showing both ends on some.

When @ 11v and 20v pp, clipping light was on constant.

[ca7922303]

Test points per schematic. Showing both ends on some.

Correction: R8 shown at (300/318vdc)

[ca7922303]

Correction: R8 shown at (300/318vdc)

Added R6(192/318vdc)

[ca7922303]

Added R6(192/318vdc)

Across J32/J33 @ 20V PP(0.8 mv)

[ca7922303]

Across J32/J33 @ 20V PP(0.8 mv)

All resistors listed are correct resistance per schematic in circuit.

[nevetslab]

Test points per schematic. Showing both ends on some.

PLEASE post photos of text so they read horizontal! I'm not one who can easily read vertical-placed text, and there are no options when you click on your photo here, without having to process each of these photos posted.

[nevetslab]

When @ 11v and 20v pp, clipping light was on constant.

AS ALL of the Clip LED drive points are in the Preamp, and I DO NOT see drive points (that liittle 'Boxed' letter P) that are everywhere in the Preamp circuits, both at tube stages as well as op amp stages thruout the Preamp), I have to conclude you're driving the power amp stage thru the preamp. What happens if you drive it from the Power Amp input jack?

You had previously stated the Preamp is working fine. When you see the RED CLIP light lit up, are you seeing CLIPPING in the Power Amp....at 11V P-P and 20V P-P?

[nevetslab]

Across J32/J33 @ 20V PP(0.8 mv)

If I understand this correctly (you have 20V PP on the outputs, meaning each buss is 10V P-P, and signal is opposite polarity on the second half output, so you have 20V P-P), and you're getting 0.8mV across J32/J33.....which is the same as the Tip and Sleeve of the insulated Output jacks......that would indicate the relays are NOT pulled in.

Earlier you show around 20mA thru the relay driver's collector resistors R46, R33, each being 1.5k/5W. So there is DC current flowing thru the relay coils for that to occur. I looked on their parts list, and see these relays are 24VDC Coils Yet you are NOT getting signal thru the relay. The relay contacts are either at GROUND potential or in contact with the Output busses.

I would unsolder the relays, and power them externally to verify each opens and closes when you energize the coils. With a 24VDC coil, you can usually get them to turn on and off with 18VDC, maybe even 15VDC, though would be weak contact. Can you do that? When unenergized, do you read 0 ohms between pins 1 and 5 of each relay, and energized, do you read the same 0 ohms between pins 1 and 4? You should hear the relay click when you energize it on/off.

[g1]

If I understand this correctly (you have 20V PP on the outputs, meaning each buss is 10V P-P, and signal is opposite polarity on the second half output, so you have 20V P-P), and you're getting 0.8mV across J32/J33.....

I was thinking the .8mV at J32/J33 was the DC there. It would be better if more details were noted.
R110 and R111 voltages should be close to same. Seems R110 voltages (and R4) are off.

Also, DC voltages should be measured without signal.

[ca7922303]

PLEASE post photos of text so they read horizontal! I'm not one who can easily read vertical-placed text, and there are no options when you click on your photo here, without having to process each of these photos posted.

[ca7922303]

AS ALL of the Clip LED drive points are in the Preamp, and I DO NOT see drive points (that liittle 'Boxed' letter P) that are everywhere in the Preamp circuits, both at tube stages as well as op amp stages thruout the Preamp), I have to conclude you're driving the power amp stage thru the preamp. What happens if you drive it from the Power Amp input jack?

You had previously stated the Preamp is working fine. When you see the RED CLIP light lit up, are you seeing CLIPPING in the Power Amp....at 11V P-P and 20V P-P?

I'll run signal thru power amp in Jack and let you know shortly.

[ca7922303]

I was thinking the .8mV at J32/J33 was the DC there. It would be better if more details were noted.
R110 and R111 voltages should be close to same. Seems R110 voltages (and R4) are off.

Also, DC voltages should be measured without signal.

I see on the schematic where it shows some test points without a note about the signal. I will go back over those and post shortly.