1. The 12AT7 (ECC81) is not for audio but more important: it sounds bad! The 6N1P is playing in a different galaxy soundwise.
2. Use a pentode as a pentode. For triode operation there are triodes🙄
3. The KT-88 sounds MUCH brighter and punchier than a EL34 or a 300B so it will be nasty wrong to use another pentode for the input.
Sorry but are you trying to sabotage his project or what?
What you mean with glassiness is the natural sound of the KT-88. Normally I would never ever replace a 6N1P with a 6GU7 or GCG7 but to the tame the KT-88 sound it is a good decision. It is so illogical to convert a Pentode to a Triode - you give away all the positive sides of the pentode. It is far better to tame the KT-88 sound with PIO caps, carbon resistors & smooth sounding valve rectifiers. Why cripple a pentode if you can get a triode for the job - I will never understand that.
I think I agree with you. 😕😀 I like pentode mode better than UL and much better than triode with this amp. Triode seems wimpy and slow with the rock I listen to. UL is good but pentode adds more of everything.
The 6CG7 is better sounding than the 6N1P in any mode with this amp, IMO. But the tube doesnt have quite enough gain except in pentode. But, I admit I am not a fan of 6N1Ps .... they sound glassy and thin to me in the numerous applications I have tried them in.
I did some research and experimentation and found the 6AQ7A (usually given the dual designation 6AQ7A/6BZ7) is the USA equivalent of the 6N1P. I tried some NOS RCA 6BQ7 vs the RCA 6CG7 and the sound is better yet. The 6AQ7/6BZ7 does have enough gain and the tube is tonally richer and more refined sounding like the 6CG7. The 6AQ7/ 6BZ7 cost all of $2 each at Radio Electric Supply. I definitely recommend trying some of the NOS 6AQ7A/6BZ7.
I am currently using a black plate Raytheon 5U4GB and this indeed adds a refinement to the sound the supplied Chinese rectifier lacked. Any of the 5U4GBs I rolled in are better than the Chinese rectifier. The Tung Sol and Raytheon black plates were my favorites.
Finally, after much experimentation with the output tubes, in this amp, using my preferred NOS input and rectifier tubes ..... the 6L6 and 6L6 varients rule. I tried Chinese KT88-98, EH KT88, SED EL34, SED 6L6GC, Russian 6P3S-E and the Tung Sol NOS 6AR6WA with tube socket adapters. I prefer any of the 6L6 types but the NOS 6AR6WA is outstanding and clearly a cut above the others to me. The SED EL34 is good in UL and this is the only non 6L6 combo I have enjoyed when not using pentode mode. If I could afford and find some NOS KT88 or EL34s maybe my opinion would be different.
My final tube combination was .....
RCA black plate 6AQ7A > 6AR6WA+ adapters > Raytheon 5U4GB
I could listen to this amp all day long with the above tube combo.
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That's the most important factor! Enjoy it!
Maybe you used too little current with the 6N1P? Or metal-film resistors? Not in this amp but in your other gear. Did you give them enough playing time? Or speakers are too harsh? Or you just love the intriguing mellow-smooth-warm sound of the old US tubes😉
Those of you who used ASC motor caps for your build, how did you attach them to the chassis? Is there a bracket you can build that lets you stand them on end?
I have all the parts on my workbench. Just waiting for some free time to start putting it together.
I have all the parts on my workbench. Just waiting for some free time to start putting it together.
I use wood for my chassis tops so all I do is cut the hole just large enough to slide the cap through then put a few large headed screws into the wood on the bottom where the screw heads catch the lip of the cap on the bottom...
You can pick those brackets up just about anywhere but I think Angela has them at a reasonable price...
You can pick those brackets up just about anywhere but I think Angela has them at a reasonable price...
What he said.
An externally hosted image should be here but it was not working when we last tested it.
I'm having trouble understanding this. Where do these 100-ohm resistors need to go if you replace the 5U4G with a 5AR4/GZ34 and what purpose do they serve?
As the poster said. On each plate of the 5AR4. Because the 5AR4 will give you a higher voltage. The resistors are to drop the extra voltage. But I would not even bother. I can't see the higher b+ hurting anything.
Sorry, I just want to make sure I understand completely. The resistor goes between secondary high voltage tap and the plate? Or does it go between the plate and the center tap?
The higher B+ is desired. MY understanding from earlier in this thread is the series plate resistors prevent overcurrent in the rectifier during startup.
I might be confused by thinking these two concepts are related.
The higher B+ is desired. MY understanding from earlier in this thread is the series plate resistors prevent overcurrent in the rectifier during startup.
I might be confused by thinking these two concepts are related.
OK, I figured out that it means in series with the transformer to the plate. Which will reduce the voltage the plate sees. It's one of those terms that people use a lot but is explained almost nowhere.
renewed interest
Hi guys,
I was interested in this project a couple of years ago and started to collect parts, but I stopped it temporarily when I decided to go on with Pass F5 (I eventually built 4 monoblocks for my biamplified system, very happy with them). Now the interest is resurfaced and I have read the entire thread again with great enjoyment and appreciation for your contributions.
I'm eager to go on with two monoblocks.
What I collected for a starting version:
2pcs Lundahl 1620/90mA output transformers
2pcs Toroidy (poland) 350-0-350V 200mA 6.3V 5A 5V 3A toroidal audio grade
2pcs EL34 Siemens '80s
2pcs 6N1P-EV nos
2pcs 5C3S Svetlana nos (like 5U4G)
ICAR and Ducati pp 450V motor run caps for power supply (60u, 30u and 10u)
2pcs Hammond 193B chokes 12H/100mA dcr 155ohm
I just need some resistors, caps and switches to be ready.
I've just one question. 5C3S heater draws 3A, unfortunately my power transformer has 3A as nominal current, so there's no headroom at all, full throttle (my fault, as it's custom built). Do you think I've to take into consideration a swap to 5AR4/GZ34 that draws 1.9A?
Cheers.
Hi guys,
I was interested in this project a couple of years ago and started to collect parts, but I stopped it temporarily when I decided to go on with Pass F5 (I eventually built 4 monoblocks for my biamplified system, very happy with them). Now the interest is resurfaced and I have read the entire thread again with great enjoyment and appreciation for your contributions.
I'm eager to go on with two monoblocks.
What I collected for a starting version:
2pcs Lundahl 1620/90mA output transformers
2pcs Toroidy (poland) 350-0-350V 200mA 6.3V 5A 5V 3A toroidal audio grade
2pcs EL34 Siemens '80s
2pcs 6N1P-EV nos
2pcs 5C3S Svetlana nos (like 5U4G)
ICAR and Ducati pp 450V motor run caps for power supply (60u, 30u and 10u)
2pcs Hammond 193B chokes 12H/100mA dcr 155ohm
I just need some resistors, caps and switches to be ready.
I've just one question. 5C3S heater draws 3A, unfortunately my power transformer has 3A as nominal current, so there's no headroom at all, full throttle (my fault, as it's custom built). Do you think I've to take into consideration a swap to 5AR4/GZ34 that draws 1.9A?
Cheers.
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Sounds like a great start for a pair of monos. I am curious how you plan to handle the front end since the original circuit only uses one half of the 6n1p per channel. Maybe a CCDA or SRPP? could be some interesting options set up as monoblocks...
D3a Driver + CCS plate load
Hi,
This is the circuit I have implemented. The driver is the D3a pentode in triode mode. The cathode resistor used was actually 180 ohms and not 250. That gives a grid (cathode) voltage of 1.8 V due to the 10ma flowing.
The IXYS chip can be obtained from Future electronics. It should be well heat sunk.
I have also tried this with a 25K/10W resistor plate load. The CCS is better.
The output transformer is 5K SE - UBT2.
Vinod
Hi,
This is the circuit I have implemented. The driver is the D3a pentode in triode mode. The cathode resistor used was actually 180 ohms and not 250. That gives a grid (cathode) voltage of 1.8 V due to the 10ma flowing.
The IXYS chip can be obtained from Future electronics. It should be well heat sunk.
I have also tried this with a 25K/10W resistor plate load. The CCS is better.
The output transformer is 5K SE - UBT2.
Vinod
Attachments
Just finished my build! It sounds incredible. Thanks very much for all of the excellent guidance.
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