Ampeg BT-15 Replacement Diodes

[fenderguy81]

I am going through a 1960s Ampeg BT-15 and noticed that one of the rectifier diodes is cracked. The schematic shows a full wave bridge rectifier made up of 1N2483 diodes, but it looks like someone had previously replaced 2 with GE5317846 diodes. Would it be ok to use the general purpose 1N4007 rectifier diodes? I have a lot of these and a few other diodes on hand already and would prefer not to have to put an order together just for a couple of diodes. Thank you!

[tubeswell]

IN2483 is rated for PIV= 400V 1A (which is a 1N4004 equivalent). So yes you can sub in a 1N4007.

[Latole]

Another schematic here ; https://ampeg.com/support/files/Schematics/B%20Series/BT-15/BT-15%20Schematics.pdf

[PRR]

Clearly says 3Amps.

Rule of thumb for totem-pole amp at 70V and 8 Ohm load suggests 1.4Amps DC which implies 2.24A of AC.

Experience shows that designers often under-specced rectifiers in those days. Today OVER-speccing is pennies.

If some fool has been steady-clipping, or plugging in 4 Ohm loads, no wonder it failed.

Nothing less than 6A 400V here. Yes, buy a pre-made bridge.

Mouser #:  583-BR104
$1.27

[fenderguy81]

Thanks for the replies! I initially put in 1N4007 diodes this morning before seeing the other schematic and other responses. It immediately blew the fuse and 1n4007 diodes. I have 1N5408 (3A, 1000v) diodes on hand, would these be sufficient enough or should I order and wait for the mouser bridge rectifier? Thanks for the input, it is greatly appreciated!

[shooter]

It immediately blew the fuse and 1n4007 diodes.

was it under load or did you have the PS disconnected from the load (tubes n such)??

[fenderguy81]

It immediately blew the fuse and 1n4007 diodes.

was it under load or did you have the PS disconnected from the load (tubes n such)??

It was under load (transistors and 8 ohm speaker).

[tubeswell]

Thanks for the replies! I initially put in 1N4007 diodes this morning before seeing the other schematic and other responses. It immediately blew the fuse and 1n4007 diodes. I have 1N5408 (3A, 1000v) diodes on hand, would these be sufficient enough or should I order and wait for the mouser bridge rectifier? Thanks for the input, it is greatly appreciated!

Oops.

[PRR]

These almost-enough rectifiers often failed at switch-on. Usually after 100 or 1000 turn-ons; that you failed at first switch suggests you have deeper problems.

When I was on salary to repair such failures, marginal design kept me employed.

[Latole]

I use heat sink clip (Soldering Heatsink / Component Holder)  when soldering diode or other fragile component.


https://www.jaycar.com.au/soldering-heatsink-component-holder/p/TD2122

[fenderguy81]

These almost-enough rectifiers often failed at switch-on. Usually after 100 or 1000 turn-ons; that you failed at first switch suggests you have deeper problems.

When I was on salary to repair such failures, marginal design kept me employed.

That’s what I’m worried about. I converted it to a 3-prong power cord and replaced all the electrolytic caps. I’m going to double check my work before powering it on again…

Here's how I rewired the 3-prong on the existing terminal strips:



Thanks for the tip Latole, I actually used that exact same heat sink clip when I installed the diodes.

[g-man]

Deleted

[fenderguy81]

Your drawing shows a 3A fuse (?) and the schematic shows a 4A fuse.

It came in “working” with a 3A fuse, but you’re correct the schematic calls for a 4A so I’ll up it to the correct size.

I looked over all of the work done and double checked it against the schematic, probed the connections with the continuity setting on my meter, and cleaned up some flux with isopropyl alcohol. Nothing appears to be causing the fuse/diodes to blow on start up. I am thinking that previously using a 3A fuse (opposed to 4A) with under rated 1A diodes (opposed to 3A) could have caused the issue? I put in the 1N5408 (3A, 1000v) diodes for now and am thinking about powering it back up and will put the previously recommended bridge rectifier on order.