Paraglow - Schottky diodes

[Bryon]

Given the problem I am having with my Paraglows, I've decided to rework/rebuild the amp replacing and upgrading as I go.  I thought I'd like to put in Cree Schottky diodes and was wondering if I should just simply replace the UF4007's and keep all the rest of the two stage power supply filters or if some or all of the filtration is rendered unnecessary by the Shottky's. 

I'd be thankful for any advice.

thanks

Bryon

[Paul Joppa]

Cool - I'll be glad to help, this should be an exciting project.

Let's see - you have the PGP8.1 power transformer, producing about 500vDC at the 2A3 plate. The UF4007 diodes were right on the edge at 1000 volts rated, so the 1200v Schottky diodes would be an excellent idea. Unless the power supply was modified, it never had a RRSF - and the Schottkys eliminate the need for one, so the identical power supply topology should work fine. This will not affect the hum, though the Schottky diodes might eliminate some buzz.

The original filter was CLC, 100uF - 10H - 100uF. That's plenty of filtering. However, as DocB has mentioned in the other thread, it would be prudent to use caps rated for more voltage than the original 450v. That's going to be your biggest difficulty, I think - hardly anyone makes 500v or 600v electrolytic caps, and they are low value - 40uF at most. And film caps are available but huge, if you stick with the original chassis, motor runs, and the like. Best reliable bet is probably series pairs of caps, 220uF rated 250 or (preferably) 350v, and with bleeders to balance the voltage drop. That's what we have in the Paramount. Perhaps a small PC board, mounted above the PGP8, could hold the Schottkys and the caps?

The other mods are pretty straightforward, but probably belong in another post for clarity.

[Paul Birkeland]

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P7456-ND

They seem to come out with new caps every few weeks...

[RPMac]

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=338-1369-ND

How about these?

[Paul Birkeland]

Very nice!  I wonder why they don't stock them. Who would order 7 of these? It's like the hot dog/hot dog bun dilemma. 

[Bryon]

Thanks for the information Paul -and for the link, Paul. 

So I take it I can just insert the Schottkys in place of the UF4007's and upgrade the 100uf caps to 500v?   

I was able to source the Panasonic TS-UP 500V caps through Digikey,ca last week- boy are they fast - ordered one day and the day after the parts are in my hands.  That's probably fairly unremarkable to those of you in major centres in the US but in the backwater of BC it is truly amazing.  When I made my order I couldn't find the 220uf 500V caps but the Paraglow parts list suggests that the 220uf cap is only 200V, so unless it was a misprint, then the 400V cap I got to replace it should be sufficient.

Although I guess one of the more important resistors would be on John Tucker's board, do you have any suggestions as to which resistors would be worth upgrading?

thanks again for your time and expertise.

Bryon

[RPMac]

Byron, the 220uf 200V cap was for the cathode bypass on the 2a3, NOT the power supply...the power supply has 100uf 450V caps. IIRC, PJ recommended at least 400V for the cat-bypass cap...I have replaced mind with the cap I posted above. (Still some bargains on the bay, if you can find them.) I have high power supply voltage also(though not quite as high as yours)...I would not recommend replacing the power supply caps with the 400V caps...to be safe, wait and get the ones Paul recommended.

Paul (either one), what would be the effect of replacing my 100uf power supply caps with the 30uf or 35uf CDE caps?

[Bryon]

Thanks for the input Robert.

I do have the 100uf 500V Panasonic TSUP caps for the power supply that Paul suggested and  realize that the 220uf caps are not the power supply caps. The link that Paul provided was for 220uf 500V caps so I wanted to make sure that I didn't need 500V in that position.

To be clear, did you replace the 220uf 200V electrolytic cap with a 35uf 500V cde film cap?  I'm sure the film sounds much better than electrolytic and I realize that the caps are +/- 20% but how does that work?

Mundorf has some film caps that could replace either the 100uf or 220uf caps if you have the space and cash.  Maybe in the next rebuild, I'll opt for a larger chassis and put these monsters in.

http://www.partsconnexion.com/capacitor_film_mundorf_mtube.html

Bryon
 

[RPMac]

Byron, I misinterpreted your post.

I had a 220uf 200V electrolytic in the 2A3 bypass position to fail. PJ recommended a higher voltage rating, so I replaced both amps with 400uf 450V electrolytics. I have now replaced those with the CDE 35uf 500V film caps. I measured the lot I got off eBay and they were all well within 5%. I may have lost some bass, but I don't know because I don't think my speakers can go low enough to tell. The mids are very clean and detailed...I may have just realized any improvement now with the new 6n1p's.

The Mundorfs look sweet!

[Grainger49]

I found an eBay seller who sold 47uF@?V (for my Paramours) that were Polypropylene Film.  They cost about $80 delivered for the four.  There just might be other sellers who have that have similar at a higher, more appropriate voltage.  It is worth a look.

[Paul Joppa]

Yes, you can just insert the Schottkys in place of the UF4007's.

The original 100uF/450v power supply caps should be replaced with at least 500v rated parts. I ran some models last night, and conclude that I would not go below 68uF for those caps - 47uF is not enough, it gives too much ripple. CDE has a variety of film caps with the mentioned "unLytic" being the smallest. I have some but have not used them yet, I imagine they would be great for the power supply but they do take up a lot of volume relative to electrolytics. (Mundorf, AVX, Solen, and others have similar products.) Since the original 450v Panasonic parts ran without problem at 500v+ for seven years, I would expect the 500v Panasonics to do well.

My calculations indicate the 2A3 cathode should be at 250v. This voltage can climb during transients, startup as well as musical, so I would be nervous about a 250v rated part - I'd go for a 250 to 400v rating. Your 400v part should do extremely well.

When we get to the main circuit updates, I will be suggesting the output transformer be returned to the 2A3 cathode instead of ground. This will keep the signal current loop out of the cathode bypass, so the sonic limitations of an electrolytic in that position will be substantially bypassed and less of a problem.

I don't know Tucker's circuit well enough to identify which resistors are most important. For what it's worth, we'll be listening to Paramounts tomorrow with the new driver boards (which can replace Tucker's board). That upgrade product should be available very soon - wanna be a beta tester?  :^)  While we're on the subject, do you want to stick with the 5965? We finally decided to use the 5670 in the Paramount upgrade, but the 5965 was very close behind. Mostly there are more tube rolling options with the 5670/2C51/396A/etc.

[Bryon]

When we get to the main circuit updates, I will be suggesting the output transformer be returned to the 2A3 cathode instead of ground. This will keep the signal current loop out of the cathode bypass, so the sonic limitations of an electrolytic in that position will be substantially bypassed and less of a problem.

Sounds great but I'm afraid you'll have to walk me through it [like I was a five year old].

...we'll be listening to Paramounts tomorrow with the new driver boards (which can replace Tucker's board). That upgrade product should be available very soon - wanna be a beta tester?  :^)  While we're on the subject, do you want to stick with the 5965? We finally decided to use the 5670 in the Paramount upgrade, but the 5965 was very close behind. Mostly there are more tube rolling options with the 5670/2C51/396A/etc.

I'd love to test the new boards.  Tucker's mods change the 5965 to a 6n1p so if I'm going to change tubes I might as well go with the your decision to use the 5670 - I do like to roll tubes.

thanks again for your continued support.

Bryon

[RPMac]

The original 100uF/450v power supply caps should be replaced with at least 500v rated parts. I ran some models last night, and conclude that I would not go below 68uF for those caps - 47uF is not enough, it gives too much ripple. CDE has a variety of film caps with the mentioned "unLytic" being the smallest. I have some but have not used them yet, I imagine they would be great for the power supply but they do take up a lot of volume relative to electrolytics. (Mundorf, AVX, Solen, and others have similar products.) Since the original 450v Panasonic parts ran without problem at 500v+ for seven years, I would expect the 500v Panasonics to do well.

What about adding a choke to the filter as CLCLC or LCLC? I have 460VDC before the filter.

[Nutube]

I am trying to kill some buzz as well
what would the specs and or part number be fo replacing the paraglow uf 4007?
thanks

[Paul Joppa]

I am trying to kill some buzz as well
what would the specs and or part number be fo replacing the paraglow uf 4007?
thanks

I think the Cree CSD05120 would work well.