Here is my KT88/120 sep amp. The circuit is the "RH Universal v2" which is very similar to Keg's schematic. I run dual rectifiers in the power supply which is on a separate chassis. The power supply is CLCLC with c1 on a switch so i can cut it out of the circuit. This allows me to have many combinations of B+ voltages to suit the power tubes . For instance, for the lowest B+ 2 5y3 and LCLC yields 330v excellent for vintage KT66 and original Tungsol 6550. Switch to 2 5ar4 , 370v. Switch in the first cap (10uf x 600v vitQ) voltages go to 440 and 480 respectively with the same rectifiers. Other rectifiers will yield slightly different voltages.Am wondering how high in plate voltage one can safely go with the KT-120 and still be able to run the 6550? Perhaps a pair of paralleled resistors and a switch would be safer.
IIRC, some of the newer PP tube amps are running above 550v on the KT-88/6550 and seem to be suffering no ill effects (shortening of tube life). Would the same be true in this application?
Also, if bumping the output to 525v would one want to bump up the OPT from 25W to 35W?
Edit: Similar question on the tube-rectified power supply. What, if any, changes would need to be done there.
Thanks.
Ooooooooooooooh!Have you seen Blue Glow build of this on You Tube?
Have you seen Blue Glow build of this on You Tube?
Hi Bob, if you want to get more into these single ended pentode amps with Schade FB resistor, you should check out the RH universal amp. Keggar, may he rest in peace, actually bases his amp's design on the RH. Here is the website;I know this thread is basically no longer active (passing of Mr. Kegger I assume?) but this has been the most wonderful archive I have come across. I have been in the process of slowly acquiring all of the parts to build a pair of SE EL34 6N1P blocks.
I have been learning about vacuum tubes for the past four years; building small synthesizer projects with tubes. This thread is invaluable. I feel more than confident that I have purchased the correct parts and my project will be successful because of everyone that has contributed to this article/thread.
Thank you, all.
-Bob K
Hi Bob, if you want to get more into these single ended pentode amps with Schade FB resistor, you should check out the RH universal amp. Keggar, may he rest in peace, actually bases his amp's design on the RH. Here is the website;
http://rh-amps.blogspot.com/2013/01/rh-universal.html
One thing that is true is that they sound amazingly good for how simple they really are. Compared to PP , push pull , amps less than half the parts. High efficiency speakers are required to get the best sound. But, in a normal living room setting most music requires only a watt or 2 for satisfactory listening level.Thanks Primo for that one as well.
Argh! Too much information! Fun information... I'm never gonna get this sucker built.
In a single ended amp the current stability is very important. Chokes by their design will deliver more current when needed, something that a resistor can not supply. A lot of diy'ers use 2 or 3 or 4 chokes in the PS. Sure you can replace the choke with a resistor but i don't believe the amp will perform as good without it. In a high powered SE amp, like the KT88 output tube, the weight of all the transformers can be massive. I usually make a 2 chassis amp with the PS on 1 chassis thus achieving better isolation between the AC nasties and magnetic anomalies away from the more sensitive circuits.Hi
I am about planning two monoblocks using kegger's mod. I would like to use solid state rectification and avoid also the choke if possible. How would a power supply for this amp look like?
Best regards
chris
Have you seen Blue Glow build of this on You Tube?
Finally getting the series running well. Should wrap it up around Thanksgiving.
Part 4 is up, working on part 5.Your KT88 videos are great. Very clear. Making me want to build another one.
Looking forward to Part 3
Hi everyone. Damn, I love this thread. I'm re-reading it once every few weeks and pick up more knowledge with each iteration.
I have a few VR90 and VR150 dudes lying around and thought it might be neat (if possible).
My "build idea" right now is the sentence, "Ooooh, that glows too? Okay, put it in!"
Using VR tubes is a neat idea. I was all set to pursue it but then i read that they can add noise to a circuit. This issue or non issue i could not verify to my satisfaction. So i let the implementation for a single ended amp aside, for now. If anyone really tried it and can give their impression pro or con, i would appreciate it.The answer is as always, "it depends". First, these tubes can supply current only up to 40mA, so you can't use them to stabilize plate current of the output tubes. One could use then to regulate G2 voltage, but original Abdellah, as well as Kegger's amps employ UltraLinear topology, where the G2 of the output tubes is connected to the UL tap of the OPT. So, if you really want to use VR tube in your amp, then I would suggest the following:
1. Add a switch that allows you to change output configuration from UL mode to full pentode mode. You will need 2 position/2 pole switch. Middle contact will go to the plate, top one to UL tap, bottom one fo VR output. Same for the other channel.
2. Using two VR150 in series to build a 300V G2 supply, as 240v provided by a VR90 and VR150 might be a tad too low.
I don’t have schematics handy with me, but if you need that I will post it later.
Cheers. Paul