BNAL said:I assume you can use the PJCCS with the headphone design?
Paul Joppa said:I think I posted on the old forum but can't find it right now. Anyhow, the problem is the battery voltage will drop as they age. Using the fixed bias of an LED in the cathode will cause an exaggerated change in tube current as the battery ages; the cathode resistor provides negative feedback at DC to maintain the appropriate operating point.
A quick look at the curves shows the plate current dropping from 2.5mA to 1.0mA as the battery drops from 36v to 24v.
A reasonable solution would be to use a current source to replace the plate load - that way the tube maintains a constant operating point, and operation will cease suddenly when the battery no longer provides sufficient compliance for the current source. I'd suggest 1.5mA as a good value to use. Note this will not work well for headphone operation where a substantial output voltage is going to be needed, unless you also add more battery voltage. Now this is starting to get complicated!
Yes, it is designed to adjust the current as the battery ages.BNAL said:I assume you can use the PJCCS with the headphone design?
No, that post is old - it's actually what started me thinking about a self-adjusting current source. The PJCCS should work well and give fairly good battery life whether implemented as a preamp or as a headpone amp with output transformer.Len said:BNAL said:
Paul Joppa said:
Would the above long post apply with the PJCCS, too?...
Paul Joppa said:No, that post is old - it's actually what started me thinking about a self-adjusting current source. The PJCCS should work well and give fairly good battery life whether implemented as a preamp or as a headpone amp with output transformer.Len said:BNAL said:
Paul Joppa said:
Would the above long post apply with the PJCCS, too?...
Yes. :^)Wanderer said:Does the PJCCS offer the same gain increase as the Hammond choke modification?
I have a choke mod Quickie and can't give up a db of gain.
cpaul said:I'm having trouble with wiring up the PJCCS I just received. The PCB is a bit different from the one pictured in the manual and some solder points are missing/not the same. The partially stuffed board is here:
http://picasaweb.google.com/103078014592468973736/Bottlehead#5537786106126040610
In short, p.13 talks about soldering a wire from points bA to bB with an "S" shaped wire. My board has no such points, though it has all other solder points in different orientations from the manual. I can't make sense of the solder points that DO exist to match them to the board as represented in the manual. Can anyone help me figure out what points are the bA and bB on my board?
Thanks.
Edit: Hnmm. I can't seem to get the pics to post, so I've tried just posting the link.
Yes, the board you have should work just fine. I'll dig up the board designs and try to describe how to hook it up, but it may take a few hours.cpaul said:Thanks, guys. In looking it over, I just assumed though different, the two boards could both be wired to work. The only issues I figured I'd have are the "s-shaped" wire connector between bA and bB and the connections to the quickie circuit. If there is a way to do this without the Queen having to send a replacement board, I'm happy to take instructions for how to wire this board properly. If all traces are visible on the board I have, I may be able to figure it out from the manual photos and schematic. If I can't work it out, I'll call her.
Oh, note too that the transistors I got don't have the metal ground plate on the back for orientation. I assumed the side opposite the one with writing was the same as the metal plate (per most transistors I've used). If anyone thinks I've got it wrong, please let me know.
Carl
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