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.
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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.
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.
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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!!
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.
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.
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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...
Regards
M. Gregg
Just joking 😀
Nice to see your progress 🙂
And development.. The case should be interesting...
Regards
M. Gregg
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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....
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....
This amplifier if used with 600 ohm Hi-Fi headphones (connected in place of the output transformers) becomes an high fidelity OTL stereo headphones amplifier.
this is the Hi-Fi version of same circuit, it works at 50V instead of 24.
The filament voltage of PL504 is 24 Vac (twisted wires), the filament voltage of ECC82 is 12Vcc stabilized by L7812CV.
The output power is about 2W per channel.
The filament voltage of PL504 is 24 Vac (twisted wires), the filament voltage of ECC82 is 12Vcc stabilized by L7812CV.
The output power is about 2W per channel.
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Very interesting..
I think I have a couple of PL500 in a box somewhere..
What coupling caps have you used?
What source are you using in the Utube clips?
Regards
M. Gregg
I think I have a couple of PL500 in a box somewhere..
What coupling caps have you used?
What source are you using in the Utube clips?
Regards
M. Gregg
I soldered the anode of PL504 directly to the wire
I used a cheap camcoder (Sony handycam DCR-SX15)
I mean where is the music coming from to the amp..Ipod etc..
Might have a go for fun..mount the PL500's horizontal..and put them in a box out of sight with mesh top and bottom.. LOL
What type of resistors have you used carbon or metal film?
Might try the HP idea with a switch to disconnect the OP Tx's and a HP socket..Not direct though 50v is a bit high for me on the HP..
Regards
M. Gregg
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