jazzbass wrote: ↑Tue Jul 16, 2024 4:56 pm
Do you think the current PT can be saved? I was thinking of adding a resistor after the choke to dissipate some voltage, what do you think?
With 500+ on the plates you need a new OT as well. 3k2 is much too low. The problem with your dropping string is that if you drop the screen node down to where it needs to be for that plate voltage, you are too low for the PI. Some sort of branched power supply could be made, but I think new transformers is the best option for EL34.
If you switch to 6L6, you could run 500V on the plates and screens, then use a dropping resistor to get the PI node down to 410 or so. The rest of the dropping resistors would be as usual. However, you will need a 4k, or better yet 4k2 OT primary, and output power might be ~70W.
Your question and the answers should be a moved to separate thread...
I understand that I have to change transformers and power tubes.....ok, I'll build a real #102, do you think a Low-Plate classic or a Hi-Plate skyliner is better?
dbharris: of course I also tried with the zenners and a circuit suggested by Martin Manning but once inserted I only got a strong background noise, a strong hum......
jazzbass wrote: ↑Tue Jul 16, 2024 4:56 pm
Do you think the current PT can be saved? I was thinking of adding a resistor after the choke to dissipate some voltage, what do you think?
With 500+ on the plates you need a new OT as well. 3k2 is much too low. The problem with your dropping string is that if you drop the screen node down to where it needs to be for that plate voltage, you are too low for the PI. Some sort of branched power supply could be made, but I think new transformers is the best option for EL34.
If you switch to 6L6, you could run 500V on the plates and screens, then use a dropping resistor to get the PI node down to 410 or so. The rest of the dropping resistors would be as usual. However, you will need a 4k, or better yet 4k2 OT primary, and output power might be ~70W.
Your question and the answers should be a moved to separate thread...
Hi Martin,
sorry for the delay but, assuming that the primary of the OT had to be at least 4k7, I no longer checked the versions of the Marshall amps that had two EL34s as finals. In order not to throw away that transformer and have to partially redo that amp anyway, I searched through the diagrams and noticed that the 50W JCM 800 had exactly those OT values, that is 4K2 primary. What do you think? I'm unsure whether to buy a new OT or keep the old one, perhaps replacing the PT.
not wanting to buy a new PT (I would prefer) I am thinking of powering the various nodes by moving one node, let me explain better: the PT after the diodes gives a voltage of 512 Volts DC, then comes the choke at its output I have 510 Volts DC and, after replacing the 2k7 Ohm resistor with a 10K 5W one, I have node B+3 438 Volts DC.
After this resistor all the voltages are in line with project #102.
B+4 331 Volts DC
B+5 321 Volts DC
The problem remains with the voltage that powers the OT which is too high. What do you think if I move the node that powers the OT of one position powering it with the next node B+3 together with the anode of the EL34?
jazzbass wrote: ↑Tue Jul 16, 2024 4:56 pm
Do you think the current PT can be saved? I was thinking of adding a resistor after the choke to dissipate some voltage, what do you think?
With 500+ on the plates you need a new OT as well. 3k2 is much too low. The problem with your dropping string is that if you drop the screen node down to where it needs to be for that plate voltage, you are too low for the PI. Some sort of branched power supply could be made, but I think new transformers is the best option for EL34.
If you switch to 6L6, you could run 500V on the plates and screens, then use a dropping resistor to get the PI node down to 410 or so. The rest of the dropping resistors would be as usual. However, you will need a 4k, or better yet 4k2 OT primary, and output power might be ~70W.
Your question and the answers should be a moved to separate thread...
