I have worked on and repaired many high power tube amplifiers in my life and never have I encountered one with such high B+ voltages.
Me yes but it comes straight from a time when the tubes were self-service and abundant.
Some French designers have pushed tubes in their last slices to get the best out of them but for a short period before being exhausted.
Some French designers have pushed tubes in their last slices to get the best out of them but for a short period before being exhausted.
I think this like the cap that is used by TdP in his cross coupled amp ...
Patrick Turner reengineered EAR 509
PT anode and cathode windings are not bifilar wound as in McIntosh, using triple insulated wire because there is
470Vdc between the two windings. The two windings do not need to be bifilar wound, because the leakage inductance
between the two windings can be eliminated by use of shunt C across ends of anode and cathode windings with the
same phase and amplitude of Vac. EAR used 22uF elcaps, but I found 2uF plastic caps were entirely adequate.
If the values in the schematic in post 39 are accurate, they are snubbers. To keep peak voltages under control if the load impedance goes too high or gets open circuited. Unfortunately, in that position you need 1100 volt caps because peaks can go that high under normal operation. IME, they tend to work just as well on the secondary, using the same values you use for a sand amp.
I had a good phone call today with the son of Oom Johan and we both agreed that I need to proceed to rework the amplifier in a simpler form. Cathode Bias and CRC psu for the small tubes. I was also delighted to have found that the Main transformer has a 470vac tap for the B+ supply.
So, I shall proceed with caution and get it going. Will keep you all posted. Thank you to each for your advice.
So, I shall proceed with caution and get it going. Will keep you all posted. Thank you to each for your advice.
deltavektor,
Great News!
You will get it up and running, it can have some of the original topology and use those nice output transformers.
It can be made to be reliable, and it should sound wonderful for many years.
Happy Building and Happy Listening!
Do keep us posted, no, don't turn it up so loud we can hear it, just tell us about it.
Great News!
You will get it up and running, it can have some of the original topology and use those nice output transformers.
It can be made to be reliable, and it should sound wonderful for many years.
Happy Building and Happy Listening!
Do keep us posted, no, don't turn it up so loud we can hear it, just tell us about it.
Why? How can you deliver precious Power with parasitic resistance near as large as load?
What looks wrong to you?
Regarding current indicated on datasheet , the higher the voltage on anodes, the lower the plate current should be , so as not to exceed max dissipation.
Regarding my comment on windings , apologies , that's just me being stupid , because of limited understanding .
Regarding my comment on windings , apologies , that's just me being stupid , because of limited understanding .
Yes, but in class AB the idle current is quite flexible, and (big slip) someone cut-off the top of that table. 2 columns are for original 6L6 (19W) and one is for 6L6GC (30W).
UPDATE - Carefully I poked around and investigated the strange behaviour of the amplifier before I decided to do anything. Found a short-circuit TIP42CG on the cathode bias board. Replaced... amplifier came to life as the designer intended! It is insanely powerful.
It is a relief that it is actually stable. It is a relief that the original circuitry actually does work stable.
One thing left that's a concern is the over-load circuit that does not remain in an OFF position after a fault has been detected.
It is a relief that it is actually stable. It is a relief that the original circuitry actually does work stable.
One thing left that's a concern is the over-load circuit that does not remain in an OFF position after a fault has been detected.
Great work, you're using sand in the right places.
I was more aggressive using 12ax7 into ksc3503 as the concertina and Mje14007 to boost the 6922 outputs to 30w .
I also am using a 3 stage transistor cap multiplier which gives surprisingly good B+ regulation as well as 120db ripple reduction.
I was more aggressive using 12ax7 into ksc3503 as the concertina and Mje14007 to boost the 6922 outputs to 30w .
I also am using a 3 stage transistor cap multiplier which gives surprisingly good B+ regulation as well as 120db ripple reduction.