Please understand I am not trying to give you a solution - just trying to make suggestions which fit with your ideas. This would be the sort of thing I would be looking at:
http://tubezone.net/pdf/diy-st70-manual.pdf
using the driver boards maybe Kt77 as output and the 1650N.
http://tubezone.net/pdf/diy-st70-manual.pdf
using the driver boards maybe Kt77 as output and the 1650N.
Sure, thank you.
I think, for now I'll decide to make this Dynaco. Maybe later I'll make some stronger amp 😉
If ST-70, I have a few questions about supply:
1. What's the total current of HV patch per channel? I mean, if I will order power transformer, what current should it deliver per channel?
2. If I remove this GZ34 tube and use a semiconductor rectifier, I should have only one winding with double courrent? I suppose the required AC voltage will be lower due to low dropdown voltage of semiconductor rectifier?
3. Can I remove this C-354 choke? I think it's not required when not using tube rectifier?
Stereo: If you are going with Hammond maybe 372HX 600V-CT should give you around 415-420V. 6A at 6.3V and 50v for the negative bias. Yes you don't need a choke but the HT caps need to be bigger.
I thought about A470 replicas: https://www.laboratoriomusicale.net...co-a470-for-st-70-4300-ct-4-8-ohm-replica-new
Maybe stupid question, but what do you mean by "600V-CT"? 2x300V in parallel? Why not just 300V with 2x higher current? And how about the HV winding current?
Maybe stupid question, but what do you mean by "600V-CT"? 2x300V in parallel? Why not just 300V with 2x higher current? And how about the HV winding current?
2x300V in series, centre tap grounded. Diode on each leg. Yep the a470 replica for the OPT is good if you are happy with the 35W per channel. I am not sure whether you want a 35W amp or a 60W amp per channel. If you use the standard transformer and remove the choke and valve rectifier you will end up with a much higher HT voltage. I think its 360-0-360 = 500Vdc = pop. I have found Hammond power transformers can buzz when hot. Also consider powering the heater for the first stage off regulated DC rather than AC. the AC can contain rectifier signals which can cause an annoying buzz in the speakers.
Lots of things to work out I guess.
Lots of things to work out I guess.
The Dyna MkIV amplifier is highly regarded, and is well worth the extra transformer/chassis cost.
Note that it is rated at 40W each.
ST-70 can get 40W too, as I saw in measurements, at 1% THD. Generally I'm intrested in achive 50W output, but A431 is too expensive for me and cant buy it locally. Alternatively, if ST70/MK4 with A470 can be tuned to get 50W, I'm intrested 😉 Even if it will reduce the bandwidth a little.
The supplies in the two Dyna amplifiers are very similar, however....
The Stereo 70 power supply has to handle 70W. The MkIV power supply has to handle 40W.
Guess which will work better?
Trying to force a tube amp to produce a little more maximum power at the cost of poorer operation is misguided.
The Stereo 70 power supply has to handle 70W. The MkIV power supply has to handle 40W.
Guess which will work better?
Trying to force a tube amp to produce a little more maximum power at the cost of poorer operation is misguided.
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ST70 is rated 2x35W (sum 70W) and MK4 is rated 1x40W (sum 40W). It's the same, or I don't know what you mean.
The power ratings of the amps are certainly not the same.
But the power supplies in the amps are the same, and one amp demands nearly twice as much power output.
Certainly the power supply with lower demands on it will work better, have lower ripple, lower hum,
lower dissipation in the rectifier, cooler transformer operation, and longer capacitor life.
Not to mention all the benefits of dual mono operation.
How is that difficult to see?
But the power supplies in the amps are the same, and one amp demands nearly twice as much power output.
Certainly the power supply with lower demands on it will work better, have lower ripple, lower hum,
lower dissipation in the rectifier, cooler transformer operation, and longer capacitor life.
Not to mention all the benefits of dual mono operation.
How is that difficult to see?
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I don't know exactly what you mean, but ST70 has a bigger transformer with 2x more current at HV winding.
If you are still interested building Dyna clones check this transformer vendor in EU. Looks good but I know nothing about them: https://www.laboratoriomusicale.net...co-a470-for-st-70-4300-ct-4-8-ohm-replica-new
Dynaco ST70 power transformer PA060 is 360-0-360Vac at 300 ma (or less); Mk4 PA-135 is 370-0-370 Vac at 150 or 160 ma.
Dynaco ST70 power transformer PA060 is 360-0-360Vac at 300 ma (or less); Mk4 PA-135 is 370-0-370 Vac at 150 or 160 ma.
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I posted the same in #65 😉
In this ST70 driver, do I really need DC balances? (500K pot with 1M to ground). Maybe can I tie cathodes together, use one cathode resistor and make a led right bias indicator as in ST70 Series 2?
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One more thing. Here: http://tubezone.net/pdf/diy-st70-manual.pdf I found a problem: on schematic, R19-R22 have 43K/2W, but in the BOM there is 47k/2W. So, which value is correct?
Only R20 and R22 are marked 43K. I think it's an error. I would go with 47K for all four.
It occurs to me that there's another possibility: In a typical long-tailed pair driver stage, like the 12BH7 used here, the two plate resistors would be slightly different to account for an inherent imbalance between the two halves of the driver. If you compare this to the Eico HF-87 schematic, which is a similar setup, R19 and R20 would be of a slightly lower value, like 43K.
https://www.ampslab.com/vintage_eico_hf87.htm
Possibly there's a mistake in the schematic AND the BOM.
OTOH, there's what appears to be a current source (or impedance source?) on the combined cathodes of the 12BH7s, which might eliminate the need for unbalanced resistors.
I would check with the designer.
https://www.ampslab.com/vintage_eico_hf87.htm
Possibly there's a mistake in the schematic AND the BOM.
OTOH, there's what appears to be a current source (or impedance source?) on the combined cathodes of the 12BH7s, which might eliminate the need for unbalanced resistors.
I would check with the designer.
The manual refers to both 12XAX7/12AU7, and 5751/12BH7, so there have been some revisions at some point that aren't consistent. Again, I would consult the designer.