Ampeg SVT CL biasing

[six el six]

I just installed a new sextet of Winged C 6550 in this amp and I can't adjust the led's on the back to get them both green. I can get one green and one red.

The amp sounds good to me but I'd like to read the current with doug's bias socket. Is that safe with this circuit?

Anyone have any experience with these?

Also, the only schematic I've found does not show the power amp at all. Does anyone have the entire schemo?

[sluckey]

The amp sounds good to me but I'd like to read the current with doug's bias socket. Is that safe with this circuit?

Should be.

Try rearranging the power tubes.

[six el six]

The amp sounds good to me but I'd like to read the current with doug's bias socket. Is that safe with this circuit?

Should be.

Try rearranging the power tubes.

I've tried that three times now. First I guessed that the back row of tubes (towards controls) would be one side of the push pull and then I tried arranging the tubes with the possibility that they were arranged left to right. Of course I don't know.

Regardless, I can't get the led's to just show green which is what the manual calls for.

On the schematic it says if both led's can't be made green then try to set them both red. That would be ok with me but the owner doesn't  know ohm's law from the ten commandments. He's just going to want his led's to be green.

So, if I could measure the current with the bias socket I'd be happier. At least I'd have an indication as to what was going on without pulling this thing open.

[six el six]

Update: Left the amp on for 20 minutes and it blew a tube.

The owner wanted winged c's and they aren't cheap.

Now I have to see if the distributor I bought the sextet from has a single that will match the set.

The disassembly to get to the problem (screen grid resistor opened) took quite a bit of time and now I've got the requisite hardware out the yin yang and molex connectors to contend with/ reassemble.

This is apparently a chinese Ampeg SVT classic.

Next time I repair one I guess I'll put spare/used tubes in first to see if it blows tubes THEN put in new ones.

[birt]

they're not easy to work on. the old SVT's are a breeze compared to the new ones.

[stratele52]

Too bad for you if a tube burn. Bias was wrong. You take a chance witout knowing how is the bias on each power tubes. How each tube work.
It look this amp really need green leds to be safe. Myself I'll check bias with bias probe and meter all the time .

It is like that we'll learn . With expensive power tube we must always be sure about bias .

[phsyconoodler]

It's a common thing to blow a tube and take out those resistors,but it's not a hard job to change them at all.Just remove all the tube socket screws and lift out the plate and the PC board without even removing the rest of the boards.Very easy once you know how.
  you can bias the amp with mismatched tubes but it's always a scary proposition cause if one tube blows it'll ruin your whole day.
And the new Classics are way easier to work on that the old hand-wired ones any day.You just need to go in armed with experience and information.

[birt]

the old ones i worked on all had connectors inside and the one new SVT i worked on was hard wired. i guess we've seen some different amps then ;-)

[phsyconoodler]

Never seen a new SVT Classic without PC boards yet.Lots of ribbon cables in between boards.
  The older 70's SVT's were hand-wired and were rats nests.But they were far superior sounding IMHO.

[six el six]

Here's some photos.

[stratele52]

It's a common thing to blow a tube 

Anybody can make a mystake but I won't say is common

[birt]

Never seen a new SVT Classic without PC boards yet.Lots of ribbon cables in between boards.
  The older 70's SVT's were hand-wired and were rats nests.But they were far superior sounding IMHO.

oh now i can see we're talking about something different. i meant the cables in between the 2 chassis.

[thermion]

the 6550 sockets are directly mounted to the PC board!?!

[birt]

yes, the same as in the SVTII and SVTII pro.