I had the pleasure of listening to this amplifier for a couple hours last night on my recently completed Tang Band 1772 speakers. All I can say is WOW this thing sounds AMAZING!!!
Great job Jim on the build and thanks Thomas for a great design! The problem now is that I'm spoiled and I WANT ONE!!! lol This is definitely the "cure for the common amp"!!
Larry
Great job Jim on the build and thanks Thomas for a great design! The problem now is that I'm spoiled and I WANT ONE!!! lol This is definitely the "cure for the common amp"!!
Larry
Hi Jeff,
You can find the schematics for 6CB5A amps on my blog. Click on the label 6CB5A for all posts related to this tube. The amp looks like the RC coupled version. There is also an interstage transformer coupled one which is a bit more sophisticated. Don't hesitate to ask me if you have any questions. I can also provide parts if you have difficulties to find what is needed.
Best regards
Thomas
You can find the schematics for 6CB5A amps on my blog. Click on the label 6CB5A for all posts related to this tube. The amp looks like the RC coupled version. There is also an interstage transformer coupled one which is a bit more sophisticated. Don't hesitate to ask me if you have any questions. I can also provide parts if you have difficulties to find what is needed.
Best regards
Thomas
6CB5 RC VERSION
Yes Thomas is right, it is the RC version which simply means it is capacitor coupled to the 6CB5 instead of the interstage transformer, this is the lower cost version, but not in all respects the power supply is a little more involved in that it has two pie filter sections with three banks of filtering all bypassed by quality mpp caps. The plate voltage on the 6CB5'S is 400v @70ma each, the 6N7'S are at 200v. All wiring is point to point with connections as short as possible, the actual chassis size is 17''x10''x3'' and it weighs approx 50lbs. I can tell you the extra choke and filtering is well worth it because this amp is dead quiet and that really also impressed everyone at the amps debut Thursday night. Oh and yes the old st shape 6CB5 are rare but I'm fortunate to have a dozen of them and I'll be looking for more, I'ts funny I had these tubes probably 15 years and never would have done anything with them had I not seen Thomas's blog so thank you Thomas!
Yes Thomas is right, it is the RC version which simply means it is capacitor coupled to the 6CB5 instead of the interstage transformer, this is the lower cost version, but not in all respects the power supply is a little more involved in that it has two pie filter sections with three banks of filtering all bypassed by quality mpp caps. The plate voltage on the 6CB5'S is 400v @70ma each, the 6N7'S are at 200v. All wiring is point to point with connections as short as possible, the actual chassis size is 17''x10''x3'' and it weighs approx 50lbs. I can tell you the extra choke and filtering is well worth it because this amp is dead quiet and that really also impressed everyone at the amps debut Thursday night. Oh and yes the old st shape 6CB5 are rare but I'm fortunate to have a dozen of them and I'll be looking for more, I'ts funny I had these tubes probably 15 years and never would have done anything with them had I not seen Thomas's blog so thank you Thomas!
Last edited:
Hi!
Yes in triode mode the voltage limit of the screen is not relevant. That is only for pentode mode when the plate could swing below screen voltage. This can never happen in triode mode. When run hot the tube delivers 7-8W in SE. 6CB5A tubes are very robust. Tube cost is low.
Best regards
Thomas
Yes in triode mode the voltage limit of the screen is not relevant. That is only for pentode mode when the plate could swing below screen voltage. This can never happen in triode mode. When run hot the tube delivers 7-8W in SE. 6CB5A tubes are very robust. Tube cost is low.
Best regards
Thomas
There are few if any sweep tubes that can eat 400+ volts on the screen.
Keep in mind that idling with no input or very low volume imposes the worst case dissipation on a Class A amp. At idle the plate and screen are at nearly the same voltage.
Look carefully into your tube after it has been sitting at idle for a minute or so to see if the screen is beginning to glow. A glowing screen will mean a short tube life and cause an unexpected runaway condition usually when idling.
Most of my 6CB5 experiments were done in push pull and even screen driven push pull. The screen is pretty rugged, but all tubes were not the same. Those experiments were several years ago and I don't remember the details.
The 6CB5 is a TV sweep tube (line output) from the first generation of color TV sets in the 1950's. I had a 1957 vintage Emerson color TV that was actually built by RCA. It used a 6CB5A. I remembered the number ad bought a bunch when this happened, they were $2 each.
http://www.diyaudio.com/forums/tubes-valves/128533-tube-sale-aes.html?highlight=tube+sale+AES
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.