Hi all,
years ago I built 2 Eiclone monoblock amplifiers, following the schematic of diytube.com, using the tube rectifier insted the solidstate, so the secondary winding of the power transformer was calculated considering the voltage drop of the GZ34.
The amps after hours of operation still sound good, but I have a higher B+ than the project data, 515V vs. 485V. How I could reduce it?
Otherwise I would switch the power tubes to Tung-Sol 6550. What to do you think of these tubes? Can be a good improvement?
Many thanks
Regards from Italy
Andrea
years ago I built 2 Eiclone monoblock amplifiers, following the schematic of diytube.com, using the tube rectifier insted the solidstate, so the secondary winding of the power transformer was calculated considering the voltage drop of the GZ34.
The amps after hours of operation still sound good, but I have a higher B+ than the project data, 515V vs. 485V. How I could reduce it?
Otherwise I would switch the power tubes to Tung-Sol 6550. What to do you think of these tubes? Can be a good improvement?
Many thanks
Regards from Italy
Andrea
Attachments
What are the specifications for your power transformers? What are the values of your first capacitor and choke now?
1. Are the transformer running hot (temperature) now? (I assume so, and that was the reason for your wanting to reduce B+) If yes, you probably don’t want to use power tubes that prefer higher plate currents than the present EL34s. That is pending the answer to the specs.
2. If your transformer specs shows you could run the required heater current (3 amp) for 5U4, try it like audiowize suggested above. For even greater reduction try 5R4 rectifiers.
3. If that doesn’t work sufficiently, you could “tune” the B+ using smaller caps in the first position after the rectifier, and/or larger chokes. (Careful about the ripple current specs of the smaller caps, perhaps use film caps if necessary) That may result in more ripple in you B+, which may need additional caps after the choke to correct.
1. Are the transformer running hot (temperature) now? (I assume so, and that was the reason for your wanting to reduce B+) If yes, you probably don’t want to use power tubes that prefer higher plate currents than the present EL34s. That is pending the answer to the specs.
2. If your transformer specs shows you could run the required heater current (3 amp) for 5U4, try it like audiowize suggested above. For even greater reduction try 5R4 rectifiers.
3. If that doesn’t work sufficiently, you could “tune” the B+ using smaller caps in the first position after the rectifier, and/or larger chokes. (Careful about the ripple current specs of the smaller caps, perhaps use film caps if necessary) That may result in more ripple in you B+, which may need additional caps after the choke to correct.
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Caution:
Changing tube types is not always recommended, without other changes:
The EL34 control grid resistor maximum spec is somewhere around 200k to 500k.
The 6550 control grid resistor maximum spec is 50k with adjustable fixed bias operation.
The 6550 control grid resistor maximum spec is 100k with self bias operation.
Failure to stay within these resistor limits, may cause the tube to go into thermal runaway, and burn things up.
And the driver stage that can drive a 200k or 500k grid resistor of an EL34,
probably will not drive a 100k or 50k grid resistor of a 6550 very well.
And the coupling cap for a 100k or 50k needs more capacitance than for a 200k or 500k resistor.
Change one thing, and 3 more need to change.
Changing tube types is not always recommended, without other changes:
The EL34 control grid resistor maximum spec is somewhere around 200k to 500k.
The 6550 control grid resistor maximum spec is 50k with adjustable fixed bias operation.
The 6550 control grid resistor maximum spec is 100k with self bias operation.
Failure to stay within these resistor limits, may cause the tube to go into thermal runaway, and burn things up.
And the driver stage that can drive a 200k or 500k grid resistor of an EL34,
probably will not drive a 100k or 50k grid resistor of a 6550 very well.
And the coupling cap for a 100k or 50k needs more capacitance than for a 200k or 500k resistor.
Change one thing, and 3 more need to change.
I've run EL34, KT77, 6550 and KT120 tubes in my Eiclones without issue, all with the stock component values. 100K control grid res, fixed bias. YMMV though. Earlier version Eiclones spec'd 0.22uF caps from the phase splitter the later version (the one I built) 0.1uF. Mine have SS rectifier, I don't remember what the B+ is. Be careful with the Hammond 156R choke, they are rated at 400 volts.
Steve
Steve
What is the voltage at the nominal 445 and 215 volt points in the PS. You might want to increase R29 to get these close to nominal if needed.
BTW, I found the Genalex KT77 (Russian reissue) works well with this amp if you don't need a lot of power. The KT120 sounded nice too, once I adjusted the bias so that each one was drawing 99mA, ~70% of their max dissipation.
S.
BTW, I found the Genalex KT77 (Russian reissue) works well with this amp if you don't need a lot of power. The KT120 sounded nice too, once I adjusted the bias so that each one was drawing 99mA, ~70% of their max dissipation.
S.
If I were doing this I would try a 5R4 rectifier first. They are less expensive than 5U4 rectifiers and provide more voltage drop. I guess in this case you will come out close to your desired B+. You have 4A in you 5V winding, so that is plenty. Easy and inexpensive to try. Unless I need more power I would enjoy my EL34s now and maybe revisit the idea when are ready to replace the power tubes.
Good luck!
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If it's a clone of an HF89, a 3K resistor would drop over 300V.
Adding series resistance in the power supply of a class AB amp is rarely desirable. A couple of 5W zener diodes in series would be a less marginal way to dump a little additional voltage without making things too saggy.
EL34 is rated 800 Volts. (More than 6550!!) While 800V would be very brave, 515V is very reasonable.
EL34 is fantastically cheaper than 6550. Like $30 to $50.
Sorry to hijack the thread...
Steve, any chance you could say which of those output tubes you preferred and why? Thanks!
Hello Steve,
thanks for your reply.
I'm happy to read you experience with Eiclone.
In fact, looking through the manual the standard design seems to be compatible with EL34, 6550, KT88 without changing.
I'm driving a pair of JBL 4312A control monitor.
What about 6550s in these amps? Sound well?
Do you suggest to replace the 156R with another one with higher rated voltage? Now, after years of operation, are working well....I hope!
In the PS I have 515V, 472V, 207V.
I don't know why the point feeding the input stage is lower. I kept the original resistors value in the PS.
Andrea
Andrea & astro:
The short answer is, read my longish review at Wallofsound.ca. See link.
A Survey of Four Sets of Power Tubes in Two Push-Pull Amps | Wall of Sound | Audio and Music Reviews
Cheers, S.
The short answer is, read my longish review at Wallofsound.ca. See link.
A Survey of Four Sets of Power Tubes in Two Push-Pull Amps | Wall of Sound | Audio and Music Reviews
Cheers, S.
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