or Connect
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › A Very Compact Hybrid Amp
New Posts  All Forums:Forum Nav:

A Very Compact Hybrid Amp - Page 111

post #1651 of 2213
Quote:
Originally Posted by Ged View Post
pin 1 voltage relative to SG 108v
pin 6 voltage relative to SG 108v
That is without the tube i trust? If so then that's fine...a bit to the higher side but still within spec.
post #1652 of 2213
yes taken with the tube removed directly from the top of the socket
post #1653 of 2213
Quote:
Originally Posted by Ged View Post
can you please tell me which one is the emitter?
The pins connected to C13P (Q4P) and C14P (Q3P).
post #1654 of 2213
Q4P and Q3P emitters are at approx 105V relative to SG
post #1655 of 2213
That's good. But I think we actually knew that from the plate B+ pin measurements. I am suspecting the buffer devices.

When you say the e12 doesn't work, do you mean that the e12 red LED comes on and stays on, correct?

Also, please double check all your solder joints and pads for bridges or clinging wire trimmings. Might be as sinple as a bad joint knocked loose during measuring.
post #1656 of 2213
Yes the LED comes on red and stays that way unlike when it initialy worked
post #1657 of 2213
Thread Starter 
I suspect the buffers too. Ged what is the voltage at pins 1 & 6 with respect to SG when a tube is inserted?

Let's get this measurement settled and then we can work on the buffers. Since OG seems to be correct we think buffers.

However, OL and OR are only hooked up to the output devices when the e12 is on. To see what's happening with the buffers we'll need to make some internal board measurements. When you're ready.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1658 of 2213
Thread Starter 
Quote:
Originally Posted by sachu View Post
I have had two CThs come back to me with issues.

1>One CTh suddenly seems to have stopped working. All voltages except for OR->SG, OL->SG seem to check out fine.
THis amp had 250 hour on it at least.
Only had time to take it apart oday..will poke around a bit more to see what's up with this amp, see what voltages are there on the splitter and the buffers and of course on the E12. (Dayton audio caps for C4R and C4L, with shunt modded alps Rk27)

2> The second CTH seems to be tripping whenever i go beond 2 o clock position on the volume knob. Need to figure out why.. (Jantzen audio caps for C4R and C4L)


Any ideas?
Sachu, what is the status of this?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1659 of 2213
V relative to SG with tube inserted is 78V on pins 1 and 6
post #1660 of 2213
Thread Starter 
OK. That's the right voltage.

We need two more measurements. R18L and R18R with respect to SG. Please measure each lead of each resistor to SG. Four measurements.


These will be a bit tricky to get, but they will tell us what the buffers are doing.

And is OG still at 12V with respect to SG?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1661 of 2213
OG is still 12v
r18r is 0.6 v and 0.6v
r18l is 11.9 v and 11.9v
post #1662 of 2213
Thread Starter 
Thanks. This means that the left channel is ok but the right is not.

I hate to go to the next step, but this will be replacing Q8R and Q9R. If this doesn't fix the problem we'll have to replace the other transistors in the right buffer. But start here.

However, before you do this please check all the resistor values in the right buffer and make sure that the opamp IC1 is really a dual opamp (TL082) and that all of its pins are seated properly in the socket.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1663 of 2213
checked your suggestions all ok
I will have to order parts for the first step but I have the other transistors on hand if we need them.
I am in absolute awe of your ability to come up with a solution and such fast responses many thanks (just keep your fingers crosssed)

Gerard
post #1664 of 2213
Thread Starter 
Thanks. We'll wait for you to get the new O/P transistors and hope that this fixes everything.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1665 of 2213
Thread Starter 
Ged, one more thing. Have you checked to see that on the right channel you have the PNP (BC327) and NPN (BC33y) devices in the correct locations? Have you checked the polarity of the other transistors on that channel?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › A Very Compact Hybrid Amp