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Hi all, I hope that you can help me out. It's more a sanity check than anything else. I picked up a Rapar hybrid PA a few weeks ago. I gave it a look over, put a mains cable on to it, put an old speaker on to the outputs (more on that later) and plugged the Jag into one of the two 6mm jacks. Worked just fine - maybe a bit quiet for 4 EL84s but that could be because I had the speaker on the 'wrong' terminals.
So I want to convert the pre-amp to a valve unit, maybe using an EF86. But I'm a bit concerned about the current capabilities of the PT. It is labelled as 130v 0.3A for the HT. this goes to a doubler to provide a HT of 260v @ 0.15A. The valves are 4 EL84s - max anode current 65ma according to the datasheet. assuming it is proper Class B (as I understand it) then maximum current draw at any one time from this quad is 130mA. The tone stack recovery and PI twin triode is a 6AQ8. Each triode has a max anode current of 10mA. Which means that at full load, the max current draw would be 150mA - the output of the doubler.
Now then, the SS pre-amp supply is a 6.3V @ 0.7A. this would easily power the heater of an EF86 (or two). So if I ditched the SS preamp I could heat an EF86 or two, but would I have enough HT current to sustain the quad, the twin triode and the input EF86 (or two)? What I'm hoping is that I have overestimated the power draw of the existing valves.
the other thing is the speaker taps of the OPT. there are four wires, going to terminals marked COM, 8, 16, 75, 100V the latter two I guess are for PA runs over long cables, so irrelevant for my purposes. If I want multitaps, is the COM the Grounded connection for both the 8Ohm and 16Ohm taps? Just checking. there is also a wire connected to the recovery triode cathode resistor that connects to the 16 terminal at the output. is this NFB? If so, why only on the 16 tap?
Oh, if you have the time, would you please check my diagram to make sure I have traced it correctly (ie there are no glaringly obvious mistakes).
As always, very many thanks for your help and support. And have a fabulous generic, secular and non-denominational holiday wherever you may be.
Paggerman
So I want to convert the pre-amp to a valve unit, maybe using an EF86. But I'm a bit concerned about the current capabilities of the PT. It is labelled as 130v 0.3A for the HT. this goes to a doubler to provide a HT of 260v @ 0.15A. The valves are 4 EL84s - max anode current 65ma according to the datasheet. assuming it is proper Class B (as I understand it) then maximum current draw at any one time from this quad is 130mA. The tone stack recovery and PI twin triode is a 6AQ8. Each triode has a max anode current of 10mA. Which means that at full load, the max current draw would be 150mA - the output of the doubler.
Now then, the SS pre-amp supply is a 6.3V @ 0.7A. this would easily power the heater of an EF86 (or two). So if I ditched the SS preamp I could heat an EF86 or two, but would I have enough HT current to sustain the quad, the twin triode and the input EF86 (or two)? What I'm hoping is that I have overestimated the power draw of the existing valves.
the other thing is the speaker taps of the OPT. there are four wires, going to terminals marked COM, 8, 16, 75, 100V the latter two I guess are for PA runs over long cables, so irrelevant for my purposes. If I want multitaps, is the COM the Grounded connection for both the 8Ohm and 16Ohm taps? Just checking. there is also a wire connected to the recovery triode cathode resistor that connects to the 16 terminal at the output. is this NFB? If so, why only on the 16 tap?
Oh, if you have the time, would you please check my diagram to make sure I have traced it correctly (ie there are no glaringly obvious mistakes).
As always, very many thanks for your help and support. And have a fabulous generic, secular and non-denominational holiday wherever you may be.
Paggerman
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