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Old 14th January 2012, 10:42 AM   #21
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by jane View Post
Max theoretical class A output power depends on the quiescent current (Iq) and the reflected load of the transformer (Rl).
Iq=35mA and Rl=600 ohm should give about 0.37 watt.
To increase otput power reduce the catode resistor of PL504 as low as 22 ohm and eventually use 4 ohm speakers, distortion wil not suffer too much.

Last edited by pilovis; 14th January 2012 at 10:45 AM.
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Old 20th January 2012, 01:05 PM   #22
pilovis is offline pilovis  Italy
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Old 20th January 2012, 01:08 PM   #23
pilovis is offline pilovis  Italy
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This is the final version of my 24Vcc tube stereo amplifier.

To increase the output power I decreased the catode resistor of the two PL504s from 56 to 39 ohm.

I also added a capacitor of 100 uF 35V in parallel to the catode resistor of the two triodes of ECC82 (higher gain).

The two output transformers you see on the picture are normal line trasformers 220v/24v 40VA, they do not saturate because of such a low anode voltage (24v) and also because they are big enough. I also choosed two transformers with higher inductance to minimize losses at low frequencies.

Note: the primary impedance of these transformers is about 800 ohm with 8 ohm load on the secondary.

Last edited by pilovis; 20th January 2012 at 01:21 PM.
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Old 20th January 2012, 01:36 PM   #24
Doz is offline Doz  United Kingdom
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That's really interesting. Especially as I have a bucket load of 24V toroidials, and two bucket loads of PL504's!!
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Old 20th January 2012, 01:46 PM   #25
pilovis is offline pilovis  Italy
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If you don't use batteries pay particular attention to the 24Vcc filtering to avoid 50/60 Hz noise.

I used a 4.700 uF 63V capacitor after the diode bridge, than i connected the secondary of an old transformer 220v/12v in series at + line as a filter inductance, and another 4.700 uF capacitor at the output.

Last edited by pilovis; 20th January 2012 at 01:55 PM.
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Old 20th January 2012, 01:50 PM   #26
M Gregg is offline M Gregg  United Kingdom
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OK I see the air variable cap where is the radio that goes with it?

Just joking

Nice to see your progress

And development.. The case should be interesting...


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M. Gregg
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Last edited by M Gregg; 20th January 2012 at 01:54 PM.
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Old 20th January 2012, 01:52 PM   #27
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by Doz View Post
That's really interesting. Especially as I have a bucket load of 24V toroidials, and two bucket loads of PL504's!!
I don't know if toroidals are suitable for this S.E. circuit.
Toroidals saturate easily with direct current and also have smaller inductance that cause low frequencies losses.

Anyway, you can try and let me know.

Last edited by pilovis; 20th January 2012 at 02:14 PM.
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Old 20th January 2012, 02:09 PM   #28
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by M Gregg View Post
OK I see the air variable cap where is the radio that goes with it?
Dead
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Old 20th January 2012, 02:33 PM   #29
Doz is offline Doz  United Kingdom
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Quote:
Originally Posted by pilovis View Post
I don't know if toroidals are suitable for this S.E. circuit.
Toroidals saturate easily with direct current and also have smaller inductance that cause low frequencies losses.

Anyway, you can try and let me know.
Point taken , back to root in the junque box !
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Old 20th January 2012, 02:49 PM   #30
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Nothing wrong with valves at low voltage...

I made a pre-amp a while back that used 6SN7, first half as gain stage and second as cathode-follower, Worked very good at only 12V...
Tried a variety of valves such as ECCxx and even Nuvistors there, but the best was a 6/30L2, gen. purpose double-triode.

As an improvement to the O/P's amp, maybe a ECC86 would be a better choice than ECC82, as it was designed for low-voltages....

A MOSFET voltage reference (Mozener) in the cathode of PL504 could give benefits in place of the cathode-resistor, and give adjustable bias too....
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