I have the original R8 from a few years ago. I was doing the mods about the time Willsenton was also watching her Youtube vids and making changes.
Willsenton R8 vs the classics
- Thread starter Gigantic
- Start date
That post is nonsense, as was the chat GTP response, the two triodes are in parallel. I don't think chat GTP or that poster understand the two grids are tied together, there is no "top and bottom". And it's not a voltage regulator, (I was initially wrong about that). It's basically a capacitance multiplier using that tube to reduce ripple.
My guess is whoever posted that, ran the two versions through chatGTP and is just parroting the wrong description it spit out too. I responded to the post, I haven't been reading or following the discussion there in ages.
My guess is whoever posted that, ran the two versions through chatGTP and is just parroting the wrong description it spit out too. I responded to the post, I haven't been reading or following the discussion there in ages.
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Jon S
Super Member
I have both the original and the "MK II" versions... The original R8 had really crappy resistors, the insulation was chipped on a lot of them. The "MK II" was a big improvement over the original.
I replaced all the caps with Mundorf Silver Gold Oils... Really liked the sound after that. The older amp was upgraded with Jantzen Superior-Z caps. The Mundorfs were a smidgen smoother.
Not sure there is much more to say about these amps that hasn't been covered in 600 pages of posts. Maybe one day I'll sit down and try to convert the input tube for lower gain.
knotscott
Super Member
I ran stock Dynaco 70s starting near 1990, then refreshed them and added some capacitance to the power supply, and ran them for over 20 years. In 2019 I added the VTA circuit board, and have since modified those even further. Great amps with tons of potential. Now I'm running two Dyna/VTA 70s as monoblocks in a bi-amp setup with a solid state Linn LK140 from 20-65hz, so the Dynas only do vocals and up. Ken Stevens from CAT has even heard them and was mildly impressed.
They're plentiful, and there are tons of options to do what you want with them. They're worthy of good caps and parts, and the VTA board supports a lot of different tube options. Hard to go wrong with stock or modified IMO.
They're plentiful, and there are tons of options to do what you want with them. They're worthy of good caps and parts, and the VTA board supports a lot of different tube options. Hard to go wrong with stock or modified IMO.
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I followed the Skunkie design - all resistors replaced with precision ones on the bias meter, and Mundorf MCap EVO coupling caps. Star ground, voltage selector deleted, PS caps, choke, headphone jack bypass, etc etc. It would be good to reduce input sensitivity as my phono stage is rather high-gain and with a MM cartridge it's too loud past around 9 o'clock.
Pretty sure @StepheK just answered that in Post 46, front end tube gain is too high. I've ran into that on other amps that had to be modified to lower the input tube gain.
Received and installed the trimmer pots, re-biased, and it's singing sweetly with Psvane 6550 outputs.
One of the boards is a little offset and more difficult to get a trimmer screwdriver on. The desoldering and resoldering went without any issue other than a couple wires broke off the boards from me manipulating them. Resoldered them and reinforced the others with some additional solder. They seem pretty brittle.
Jon S
Super Member
Yep, they are... The same thing happened to me... After putting it back together, all was fine for about a week then all of a sudden, one channel stopped working... I thought, oh oh, I screwed up. After disassembling the amp, one of the bias board wires was broken off from the board.
FYI, the R8 is VERY sensitive to noisy front-end tubes. That is what is causing the scratchy sound from the speakers when adjusting the volume. I noticed that some tubes have no issues, some do. It does not matter if the tube is brand spanking new or vintage. I'd say 60% of the tubes I have are noisy.
FYI, the R8 is VERY sensitive to noisy front-end tubes. That is what is causing the scratchy sound from the speakers when adjusting the volume. I noticed that some tubes have no issues, some do. It does not matter if the tube is brand spanking new or vintage. I'd say 60% of the tubes I have are noisy.
I had that scratchy noise until I went to Sylvania and National front-end tubes, and now the volume control is silent. Next time I'm in the amp I'll probably replace the thin wires going to the bias boards.
It's quite a remarkable and good-looking amp and is easy to work on. It's always a bit nerve-wracking when you button it up after a significant change, power it on, and see the bias meter pegged even though I ohmed out the old&new pots. A slight turn of the pot put the meter right on center, and after running in for an hour I re-biased and played some records.
Also the voltage out of the center tube is a bit high in the 230s and I want to experiment with resistor values to get it to 225v.
It's quite a remarkable and good-looking amp and is easy to work on. It's always a bit nerve-wracking when you button it up after a significant change, power it on, and see the bias meter pegged even though I ohmed out the old&new pots. A slight turn of the pot put the meter right on center, and after running in for an hour I re-biased and played some records.
Also the voltage out of the center tube is a bit high in the 230s and I want to experiment with resistor values to get it to 225v.
Jon S
Super Member
Yeah, the Willsenton is very sensitive to noisy tubes because of their high gain design...
Word of advice, when replacing the power tubes, make sure you turn the bias pots to the minimum value (all the way counter-clockwise) before powering the amplifier on. Tubes have different plate measurements and the old tube might have a higher bias adjustment than the newer one. I lost a EL34 because the bias point on the new tube was lower than the older tube. When I powered the amp on and started biasing the new tubes, one of the new tubes red-plated on me because the bias adjustment was too high. The bias meter was pegged to the right which fried the tube with the high current. I guess some tubes are more sensitive to too much current going through the tubes.
Learned this the hard way... makes me wonder about these amplifies which have auto-bias. The same could happen while the amplifier is auto-biasing.
Word of advice, when replacing the power tubes, make sure you turn the bias pots to the minimum value (all the way counter-clockwise) before powering the amplifier on. Tubes have different plate measurements and the old tube might have a higher bias adjustment than the newer one. I lost a EL34 because the bias point on the new tube was lower than the older tube. When I powered the amp on and started biasing the new tubes, one of the new tubes red-plated on me because the bias adjustment was too high. The bias meter was pegged to the right which fried the tube with the high current. I guess some tubes are more sensitive to too much current going through the tubes.
Learned this the hard way... makes me wonder about these amplifies which have auto-bias. The same could happen while the amplifier is auto-biasing.