ph204 diodes?

[BobSimpson]

I've got a yba-1 with a physically split PH204 diode.
I've not been able to source one, but the net says 1N4007 is an equivalent.

I'd prefer to find an real PH204.
If I have to go the 4007 route, should I replace all 4 PH204's?

Bob Simpson

[xtian]

Modern silicon is so much superior to old stuff. Why would you want to go back to dark ages?

[thetragichero]

to piggyback off that, i like the 1n4937 from say tayda help remove switching noise
yes replace all of them

[Stevem]

If you stay with the old school 204 or 1n4007 atleast bypass each one with a .01 600 volt ciramic disc cap to reduce switching noise.

My fav pick for a modern fast switching recto is the UF5408.

With amps that use 6 diodes you only need 4 UF5408s, ( non bridge recto amps ) with amps that use 4 diodes you only need 2 UF5408s.

[turbofeedus]

If you stay with the old school 204 or 1n4007 atleast bypass each one with a .01 600 volt ciramic disc cap to reduce switching noise.

My fav pick for a modern fast switching recto is the UF5408.

With amps that use 6 diodes you only need 4 UF5408s, ( non bridge recto amps ) with amps that use 4 diodes you only need 2 UF5408s.

I've used these on several amps now, no switching noise to speak of.
OP, there are times to "stay original", and times to go modern. Rectifier diodes are 100% the latter.

[pdf64]

...With amps that use 6 diodes you only need 4 UF5408s, ( non bridge recto amps ) with amps that use 4 diodes you only need 2 UF5408s.

To accommodate foreseeable scenarios such as high mains and low loading, with 1kV diodes, they will need putting in series pairs if, as with many amps, the HT winding voltage is much over 600Vac.

[R.G.]

Some caveats about using series devices for high voltage tolerance. In series capacitances and diodes, you need to think just a little about how the voltage divides.

Series diodes will divide an applied DC voltage by the inverse of their leakages. If one is leakier than the other(s) it supports less than its share of the voltage. This can lead to the leaky diode letting the breakover of the low leakage diode be exceeded, shorting it, and then the high leakage diode is itself killed. This problem is often solved by paralleling the diodes with high value resistors which will "leak" about ten or more times current than the highest leakage diode. The reverse voltages are then nearly equal and you can't get the chain failure syndrome. Series caps do much the same thing. Both need leakage swamping resistors to equalize the voltages in some situations.

Diodes can have dynamic failures if their turn on/off behavior doesn't track. This is the same failure scenario as above, but with spikes at turn on and turn off. The same paralleled caps to suppress switching noise work, and if the caps are much bigger than the diode and stray capacitance, they form a capacitive voltage divider to ensure the voltage distribution is within bounds.

[didit]

Hello -

Recent research lead to these DGP15 -- https://www.vishay.com/docs/88567/cgp15.pdf. Avoids any series diode string for all but insane voltage level designs. Not super fast, though adequate.

Best .. Ian

[Hawkbone]

hi all, I'm new here. I've been recently bitten by the tube amp bug. Bought a Yba-1a last year and I'm in love with it lol. Just bought a 72 Yba-4 that has had very little work done on it - just bias caps and V1 socket replaced as far as I can tell. So, time to install a 3 prong cord & replace the filter caps. While I'm at it I'll renew the bias caps and rectifier diodes. I can see from the above discussion that there are some alternatives for diodes and that I may not need to replace all 4 rectifier ones. So a couple questions pop to mind - 1) is it ok to replace all diodes anyway? Or is there any point? I see that a previous owner had the 6x diodes of the YBA-1a replaced with just 4 2) Which diode should I get and does anyone have a good online source for them here in Canada?

Thanks in advance!

hawk

Schematic in amp.jpg

20210419_104622.jpg

[Phil_S]

Looks like I'm late to the party. According to the schematic, high voltage is 440VDC. I would not be overly concerned about which 1KV or higher rated diodes are chosen. You received good advice from others on this. I would replace all the diodes so that they are all at the same spec. Diodes are cheap parts. 1N4007 run about 10/$1 in the US. I imagine UF5408's could be as much as $1 CAN each. You won't go broke getting diodes. I think that Digikey and Mouser have an online Canadian catalog. You' might pay more for shipping than you do for merchandise. If you are willing and have some time to allow for shipping, you might source them from eBay where they will be dirt cheap. Otherwise, you should wait to see if one of our Canadian friends here will make a suggestion.

That's a real antique you have there. Congratulations on the acquisition. Yes, time for an overall cap job. Go for it.

[Hawkbone]

hey thanks Phil. There is good advice above but I'm not sure I understand it

I'm happy to replace all that needs replacing without much consideration to cost as this amp deserves a new lease on life. I'm mostly confused with the statement above that I can remove the 4 old rectifier diodes and replace with just 2 new ones. My gut says it would be easier to just swap in new diodes of similar or better spec and keep the layout the same. Then again, my gut used to like some horrible beer so I don't always trust it. Am I ok getting say 5x UF5408-E3/73 to replace the 5x pH204 or do I need to reconfigure the circuit slightly using just 3x UF5408-E3/73?

cheers, hawk

[sluckey]

There is no reason to replace any diodes unless they are defective. Silicon diodes don't gradually go bad. They are either good or they are bad, no weak inbetweeners. If they are working, leave them alone. Keep the vintage look of the bullets. And since the YBA-4 uses a FWB you cannot replace four diodes with two.

[Hawkbone]

Thanks Sluckey. I couldn't understand how I'd replace 4 with 2 as each diode seems to be an essential link in the circuit. Ok I'll do the power cord and caps, clean up as much as I can - good layer of nicotine on everything and it's like a shellac! -then power up and see what I got. PO used the amp recently so I don't think there are any major issues besides lack of ground. Cap replacement seems to be just good practice but I stand to be corrected on that too.

cheers, hawk

[Hawkbone]

Not sure if the board warpage is an issue I need to deal with

20210419_104640.jpg

[sluckey]

No problem. It got warped when it was originally screwed to the chassis.