Afterglow - now I really mean it!

[Paul Joppa]

You can't get a 600-volt electrolytic. 100uF 700v film caps exist but they are pretty darn big! Yes, one resistor across each cap.

[Paul Joppa]

One further note - in the adjacent thread on a Paraglow II, PB recommends a particular Ohmite 50-watt resistor. This resistor is available in a 4Kohm version, which would be closer to the value you need for the Afterglow/PGP8.1.

The thread is at https://forum.bottlehead.com/index.php?topic=12403.0

Kind of funny that there are two such similar threads on amps more than 20 years old, at the same time, and just when I was digging out the history.

[pboser]

Thanks - I was trying to figure out what resistor to get. 
Yes, that is funny.  Lots of Bottlehead legacy product loyalty!
Thanks again!

[pboser]

Okay, today I received the recommended big Ohmite resistors for the output tube cathode resistor, along with mounting brackets.  Now to figure out where to mount them - any suggestions?  I saw PB's photo on the other thread, but I'm hoping to stick with the 10x6 chassis I have.
Thanks!

[Paul Birkeland]

They make little metal brackets to hold those big tubular resistors.  If you need help finding them, I can help you look them up.  You can just use wood screws and mount that resistor right onto the wood base.  My experience with that part is that part running 60mA through it is that it sits around 150F, which isn't that big of a deal for proximity to wood.  The little mounting brackets will keep it spaced off about 3/16" anyway.

[pboser]

Hi Paul,
That sounds much easier than finding a place on the chassis!
Fortunately, I spent quite a while on the Mouser site and looking at Ohmite's linked documents and I think i got the right brackets.
I'll work on that while I await the other parts. Progress!
As always, thanks!
Pete

[pboser]

I finally got the rest of my parts and got started last night.  I should be able to finish up this evening. Any suggestions on testing before I assume it's ready to go?  I have the Afterglow manual, and could do the testing there, though I assume a few voltages will be different.
I'm champing at the bit!  Thanks again for the help.
Pete

[Paul Birkeland]

My only suggestion for testing is to use the cheapest possible 2A3 that you can find!

[Paul Joppa]

My biggest uncertainty is the 2A3 voltages, so I'd like to see the DC voltages at each pin of the 2A3 socket.

[pboser]

Now you’re making me nervous! I think I’m down to one pair of rca 2a3s. Is there any value in making measurements without the output tubes in?

[Paul Birkeland]

So, you could fire the amp with no 2A3, but the driver tube won't work without it.  This would just be something you'd do to be sure the power supply is wired correctly. 

I'd snag a Sovtek or two for testing:
https://www.ebay.com/itm/NIB-new-Sovtek-2A3-vacuumt-tubes-51-each-matched-pairs-or-quad-available/402220779030?hash=item5da63a0616:g:eYgAAOSw1tVek5Xy

[pboser]

I looked around the house and found an Electro Harmonix (Sovtek, right?) 300B and a pair of Sovtek 6B4G, but no other 2A3s, so I think I'll take your advice to be cautious and get some new 2A3s for testing purposes.  More waiting to hear the amp, but it seems smart to play it safe. Thank you gents.

[pboser]

Got the tubes - NOS Arcturus 5965s and new Sovtek 2a3s.  Plugged them in and here's what I got for voltages on the output tubes:

Pin 1- 189/219
Pin 2 - 452/443
Pin 3 - 139/178
Pin 4 - 189/221

So, what gives?

As always, thanks in advance for your support and help.
Pete

[pboser]

After sending the note above I had the idea to swap the tubes and see what happened.  I swapped both the 5965s and the 2a3s.
When I did so and turned the amps on, the second one had no audio!  Here are the voltages:

220/102
442/479
179/19(!)
220/102

What did I do?!?!

[Paul Birkeland]

Pin 1- 189/219
Pin 2 - 452/443
Pin 3 - 139/178
Pin 4 - 189/221

What do the slashes mean?  Is that 189 on one amp and 219 on the other?