I was listening to it last night and something didn't seem quite right. It's like there is separation and not real warm sounding. I checked the tubes on my other tester, a U-Test-Em, and one of the power tubes failed.
I have some 6L6, EL34 and 6V6. Can I sub them if I change the rectifier to a 5U4? If I can, would the bias till be 1.56? Thanks
I have some 6L6, EL34 and 6V6. Can I sub them if I change the rectifier to a 5U4? If I can, would the bias till be 1.56? Thanks
Use the EL-34 if possible. Or if you have a pair of 6L6, they will function if the bias is adjusted.
The 5AR4 is better, but the 5U4 will do for the rectifier if necessary, but has no time delay
and more voltage drop. so adjust the bias again. Use 1.56V (50mA plate current each) always.
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What I gathered looking for an answer to post #41 was that the 5U4 with more voltage drop was necessary for proper plate voltage to the EL84. If this is not necessary, can I insert the EL84 or 6L6, leaving the 5AR4 in place, and just adjust the bias? I've looked for answer before posting and come up dry. Thank you
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Do you mean the EL-34, which is a very different tube from the EL-84.
The EL-84 is neither mechanically nor electrically compatible with the Stereo 70 amp.
You can use the 6L6 in pairs with either rectifier if you adjust the bias.
The 5AR4 should work ok with the 6L6 tubes, no need to get a 5U4.
The Stereo 70 amp is designed for the EL-34, and works best with matched pairs of that tube.
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Thanks for this. You have no idea how longed I searched for this answer
I'm sorry yes EL34, It's a Mark III btw
In that case, the HV in the Dyna MKIII amplifier is much larger.
Only the 5AR4 rectifier will work properly in this amp.
Output tubes that will work are: matched pair 6550 or matched pair KT88.
The bias must be properly adjusted per the manual.
Turn the bias pot to minimum before turning the amp on, after replacing the tubes.
https://hafler.com/pdf/dynaco/DYNA-mark3.pdf
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What I was searching for was the bias voltage if I swapped in some alternative tubes. Since there aren't any alternative tube workarounds, KT88 and 6550 notwithstanding, the point is moot for me.
Is the bias setting amp specific or do all 6550 or KT88 have a 1.56 bias?
Is the bias setting amp specific or do all 6550 or KT88 have a 1.56 bias?
The Dyna MKIII is designed for 1.56VDC with the allowed tubes, 6550 or KT-88.
The 1.56VDC is actually 140mA (70mA + 70mA) through the 11.2 Ohm resistor.
Use only a matched pair of output tubes in this amp.
In your opinion what are those most "musical" or have the best tonality, KT88 or 6550 in your opinion? I'm not concerned about power.
Are there certain capacitors that express more tone? I used Vishay underneath and Sprague on the board. I see people talking about Mullard Mustards, Sozo, Orange Drop, etc. and StudioElectronics sells Meic. opinion on that?
Are there certain capacitors that express more tone? I used Vishay underneath and Sprague on the board. I see people talking about Mullard Mustards, Sozo, Orange Drop, etc. and StudioElectronics sells Meic. opinion on that?
The tubes vary brand to brand, so it's hard to be sure. Stay with a major mfr with a warranty.
Buy only matched pairs.
Use only new, brand name capacitors, no NOS parts. Is this for use in a guitar amp?
If so, the Sprague 716 series is popular, reliable, inexpensive, and they have copper leads.
Buy only matched pairs.
Use only new, brand name capacitors, no NOS parts. Is this for use in a guitar amp?
If so, the Sprague 716 series is popular, reliable, inexpensive, and they have copper leads.
That's why I was asking about the tubes because I have no experience with the different brands and such.
Since I have a failing tube, it's hard to judge, but it seems like it is overly bright. That's why I asked about the caps. It needs more low end. Hopefully replacing the bad tube will help. That's why I was wondering which tube manufacturers or types(KT88 or 6550) have a low end bias.
Bass will be best when using a well matched pair of output tubes, to minimize the DC in the output transformer. The coupling capacitors to the output tube grids are likely to be leaking, so replace them with brand new (NOT with NOS) film capacitors.
These are the lowest cost I've seen, and have a 90 day warranty.
https://www.tubesandmore.com/products/vacuum-tube-6550we-sovtek
Viva has them cheaper: https://www.vivatubes.com/new-matched-pair-2-sovtek-6550we-vacuum-tubes/
but frankly, I'd go with PSVANE instead of Sovtek - and they have a 1 year warranty! https://www.vivatubes.com/new-matched-pair-2-psvane-kt88-hi-fi-series-vacuum-tubes/
And they will be on sale again on boxing day I think...
but frankly, I'd go with PSVANE instead of Sovtek - and they have a 1 year warranty! https://www.vivatubes.com/new-matched-pair-2-psvane-kt88-hi-fi-series-vacuum-tubes/
And they will be on sale again on boxing day I think...
I've replaced the capacitors on the pcb with Sprague 418 and 715. I didn't see the Orange Drops in .25uF on Mouser when I ordered them. They are all orange, though.
I guess folks have put another bias pot on there so you don't have to replace both tubes every time, huh?
Edit: Something like a knob on a car radio where the inside and outside adjust different parameters. That way you don't have to drill holes.
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The standard capacitor value will be 0.22uF instead of 0.25uF. The 715P has steel leads,
and not copper like the 716P.
With a separate bias adjustment pot for each tube, the DC bias current in each output tube
can be made equal. This minimizes the DC in the output transformer, which is always a good thing.
But you should still buy matched pairs for best results.
If one tube goes, get a new matched pair, and keep the one good tube as an emergency spare.
Yes, definitely. In olden times, caps had much worse tolerances, and fewer available values.
Now they are more stable, accurate, and made in more values.
The original 1955 Dyna circuit has 0.25uF and 100k on the output tubes, setting a rolloff at 6.4Hz.
Using 0,22uF instead just changes that to 7.2Hz, which is not a significant difference.
Would that be like changing the crossover point in a speaker?
How about these Angela's for $29 apiece!! Ouch. Not the correct capacitance, I know.
Edit: fixed price
Not really, it's just where the bass response rolls off. That's way below where any speaker rolls off.
And it's inside a feedback loop, so the measured response will barely change, if at all.
The new capacitor is polypropylene, not paper, so it does not leak and mess up the grid voltage.
And it will sound better than the old paper one, too.