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is there any difference
- Thread starter 1iwilly
- Start date
Any distinctions?
Yeah.
As to what they are? Never have come up with a proper record of which revision level came with which front panel/cover combination. Got used to taking off the top and bottom covers to see what's there.
The HV in the original versions had an open-frame relay that closed the circuit between the power transformer's HV winding and the rectifier when you key the mike. Served to put the tubes on standby by shutting off the HV. Was originally mounted on the rear corner of the HV rectifier/filter cap board underneath. Later it was located on the underside of the chassis just frontwards from the final tubes and wired in line with the 800 Volt DC supply, not the AC from the transformer. Later versions got rid of that relay altogether, using negative grid bias alone to place the tubes in standby.
There were never any serial numbers on this model, so you can't use that as guidance to what's on the inside.
The one in your pic is the earlier version of the preamp/keying circuit, pretty sure. Later production had a circuit board with one plug-in relay and two low-profile sealed relays mounted to the chassis deck directly beneath the Load control. That pc board has all the wires soldered to it.
And if someone says the plug-in relay board was the later one, I could be wrong about that.
Maybe.
The high voltage came from either a rectangular epoxy block with a full-wave bridge rectifier in it, or a set of four 3-Amp rectifier diodes in a full-wave voltage doubler circuit. Naturally the transformer that matched the bridge rectifier delivered twice the AC voltage for the tubes' HV as the one meant to use with the full-wave doubler circuit. No markings will reveal a hint as to which transformer is which. Likewise you have to remove the bottom cover and scrutinize the HV circuit board in the center if you want to know which of the two versions you have. Just don't plug the higher-voltage transformer version into the lower-voltage amplifier deck. Sparks, smoke and massive disappointment will follow. And if you mismatch them the other way, you have an amplifier that's perpetually on Low side, no matter which way you throw the High/Low switch.
Most production versions have an input-matching coil and trimmer cap attached to the rear of the High/Low switch. It will be active in Low side only. The factory schematic just shows the radio's drive going directly to the cathodes of the final tubes with no matching circuit. I don't think they built too many of them before that detail was added.
73
Yeah.
As to what they are? Never have come up with a proper record of which revision level came with which front panel/cover combination. Got used to taking off the top and bottom covers to see what's there.
The HV in the original versions had an open-frame relay that closed the circuit between the power transformer's HV winding and the rectifier when you key the mike. Served to put the tubes on standby by shutting off the HV. Was originally mounted on the rear corner of the HV rectifier/filter cap board underneath. Later it was located on the underside of the chassis just frontwards from the final tubes and wired in line with the 800 Volt DC supply, not the AC from the transformer. Later versions got rid of that relay altogether, using negative grid bias alone to place the tubes in standby.
There were never any serial numbers on this model, so you can't use that as guidance to what's on the inside.
The one in your pic is the earlier version of the preamp/keying circuit, pretty sure. Later production had a circuit board with one plug-in relay and two low-profile sealed relays mounted to the chassis deck directly beneath the Load control. That pc board has all the wires soldered to it.
And if someone says the plug-in relay board was the later one, I could be wrong about that.
Maybe.
The high voltage came from either a rectangular epoxy block with a full-wave bridge rectifier in it, or a set of four 3-Amp rectifier diodes in a full-wave voltage doubler circuit. Naturally the transformer that matched the bridge rectifier delivered twice the AC voltage for the tubes' HV as the one meant to use with the full-wave doubler circuit. No markings will reveal a hint as to which transformer is which. Likewise you have to remove the bottom cover and scrutinize the HV circuit board in the center if you want to know which of the two versions you have. Just don't plug the higher-voltage transformer version into the lower-voltage amplifier deck. Sparks, smoke and massive disappointment will follow. And if you mismatch them the other way, you have an amplifier that's perpetually on Low side, no matter which way you throw the High/Low switch.
Most production versions have an input-matching coil and trimmer cap attached to the rear of the High/Low switch. It will be active in Low side only. The factory schematic just shows the radio's drive going directly to the cathodes of the final tubes with no matching circuit. I don't think they built too many of them before that detail was added.
73
