ok..think im sorta bamboozled!

by dmagazz Wed Jun 27, 2018 5:40 pm

dmagazz: Posts : 147
Join date : 2018-06-20
Age : 57
Location : new fairf, ct

Post n°1

ok..think im sorta bamboozled!

by dmagazz Wed Jun 27, 2018 5:40 pm

i got this kit off fleabay. listed as NOS. (new old stock)
they called this thing ...brand, SCC, DYNACO (DYNAKIT) ST70 Tube Amplifier Diode Kit (replaces the selenium diode)D544042R)
well it has no resistors, capacitors either. has a 2 lug standoff,a screw and nut to secure the standoff, and a 544015 GI536 diode that has friggin been tinned on the ends /obviously soldered to something at one time.
so its not new old stock, its used possibly incomplete.
came with a vague diagram.
does anyone know if this 544015 GI536 diode is even a match for the 1n4007?
or even was it actually a dynaco kit at one time?
it may be D5 in the circuit of an ST 70II by the looks of my findings
at least my meter shows .873 k ohms in direction forward and infinity reverse. so it seems it checks ok.
i think its a NTE552, but not 100% positive.

by **Bob Latino** Wed Jun 27, 2018 6:57 pm

Bob Latino

Bob Latino: Admin; Posts : 3277
Join date : 2008-11-26
Location : Massachusetts

Post n°2

Re: ok..think im sorta bamboozled!

by Bob Latino Wed Jun 27, 2018 6:57 pm

That diode will only look at about 55 VAC so most likely ANY diode will work in this situation. Just make sure that the RED/BLACK wire from the power transformer is connected to the banded end of the diode and you will be OK. The one caveat with replacing the selenium rectifier with a diode is that a diode has more forward voltage that a selenium rectifier and the range of the bias system will be "off" just a little, To correct this you should parallel the two 10K resistors on the 7 lug terminal strip with two other 10K resistors effectively giving you two 5K resistors. This will allow biasing the two output tubes per channel more near the center of the bias pot's range. It's too bad Dynaco chose a 10K pot here. A 20K pot would allow more latitude for biasing a wider variety of output tubes.

Bob

by dmagazz Wed Jun 27, 2018 7:07 pm

dmagazz

dmagazz: Posts : 147
Join date : 2018-06-20
Age : 57
Location : new fairf, ct

Post n°3

Re: ok..think im sorta bamboozled!

by dmagazz Wed Jun 27, 2018 7:07 pm

ok, so this will be ok t replace the selenium diode in my 1966 st 70 then
would you say 1 watt or 2 watt resistors bob?
oops, i just realized it still has the 50v bios capacitors
thanks for ringing in by the way, i appreciate it.

by **Bob Latino** Wed Jun 27, 2018 7:30 pm

Bob Latino

Bob Latino: Admin; Posts : 3277
Join date : 2008-11-26
Location : Massachusetts

Post n°4

Re: ok..think im sorta bamboozled!

by Bob Latino Wed Jun 27, 2018 7:30 pm

dmagazz wrote:ok, so this will be ok t replace the selenium diode in my 1966 st 70 then
would you say 1 watt or 2 watt resistors bob?
oops, i just realized it still has the 50v bios capacitors
thanks for ringing in by the way, i appreciate it.

One watt resistors would be fine in this case .. Maybe even a 1/2 watt would work OK? I would replace those 50V caps on the 7 lug terminal strip with 100 volt caps. Make sure that you get the polarity of these caps correct when you install new ones ..

Bob