replacing the tube rectifier 5ar4 simply means a savings of around 12 watts of power, power that is now available for the output tubes, and that is just 3 watts a piece, not too much i think...
if the el34's were running 14 watts per plate, that is an increase to 17 watts, not too much either....
if the el34's were running 14 watts per plate, that is an increase to 17 watts, not too much either....
Or, just reduce the size of the first B+ capacitor. Lower peak currents, no heater consumption, adjustable for modern AC power line voltages. Fairly painless.
All good fortune,
Chris
Many many years ago I replaced a failed PA60 power transformer in a 1970's vintage Dynaco ST70 with a reissue power transformer from Triode Electronics of Chicago. This was in the mid 1990's if I remember correctly.
At that time the Triode Electronics PA60 replacement was specially made to provide the original factory B+ voltage with solid state diodes. It did NOT have a 5V filament winding for a rectifier tube. It was also taller and heavier than the original power transformer and it still works perfectly, 25 years later. It barely gets warm.
I just dug this ST70 amp out of storage and I will run some measurements on it and post the B+ voltage and output tube bias voltages/currents here after I check it out.
Triode Electronics is still around, and they still specialize in high-quality replacement transformers for Dynaco and for almost every tube/valve guitar amplifier in existence:
POWER TRANSFORMERS - MADE IN USA
However, the current production Triode Electronics replacement PA60 for the ST70 is more like a heavy-duty version of the original Dynaco PA-060, with the 5V filament winding for the GZ34/5AR4 rectifier. So it might generate excessive B+ voltage when used with diodes rather than a valve rectifier:
PA060 S Dynaco ST70 Upgrade Power Transformer Replacement MADE IN USA
There are plenty of designs and drop-in products to replace tube/valve rectifier tubes with diodes. Some of them are just 2 diodes inside a plastic tube base. Others include a series resistor.
I've had some thoughts about measuring a bunch of actual GZ34/5AR4 tubes under load and then designing a solid-state replacement that has the same voltage drop and voltage vs. current characteristics as an original GZ34/5AR4.
I think it would be challenging to duplicate the original "slow turn on" characteristic of an actual tube/valve rectifier. However, I haven't observed a higher failure rate of EL34 otuput tubes during 25+ years of using my ST70 with a solid-stage rectifier. So perhaps the slow turn-on isn't needed for EL34 output tubes?
-EB
At that time the Triode Electronics PA60 replacement was specially made to provide the original factory B+ voltage with solid state diodes. It did NOT have a 5V filament winding for a rectifier tube. It was also taller and heavier than the original power transformer and it still works perfectly, 25 years later. It barely gets warm.
I just dug this ST70 amp out of storage and I will run some measurements on it and post the B+ voltage and output tube bias voltages/currents here after I check it out.
Triode Electronics is still around, and they still specialize in high-quality replacement transformers for Dynaco and for almost every tube/valve guitar amplifier in existence:
POWER TRANSFORMERS - MADE IN USA
However, the current production Triode Electronics replacement PA60 for the ST70 is more like a heavy-duty version of the original Dynaco PA-060, with the 5V filament winding for the GZ34/5AR4 rectifier. So it might generate excessive B+ voltage when used with diodes rather than a valve rectifier:
PA060 S Dynaco ST70 Upgrade Power Transformer Replacement MADE IN USA
There are plenty of designs and drop-in products to replace tube/valve rectifier tubes with diodes. Some of them are just 2 diodes inside a plastic tube base. Others include a series resistor.
I've had some thoughts about measuring a bunch of actual GZ34/5AR4 tubes under load and then designing a solid-state replacement that has the same voltage drop and voltage vs. current characteristics as an original GZ34/5AR4.
I think it would be challenging to duplicate the original "slow turn on" characteristic of an actual tube/valve rectifier. However, I haven't observed a higher failure rate of EL34 otuput tubes during 25+ years of using my ST70 with a solid-stage rectifier. So perhaps the slow turn-on isn't needed for EL34 output tubes?
-EB
The slow turn-on ( aka B+ delay) don't bother tubes. Not at the low voltages present.
A harsh sudden turn-on however might stress tubes due to surging coupling caps ( that is
if the turn-on occurs after the filements are warm)
A harsh sudden turn-on however might stress tubes due to surging coupling caps ( that is
if the turn-on occurs after the filements are warm)
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