Hello,
a Couple years ago i picked up this cute little Graymark 509 Amp kit off eBay. I have not had a real use for it but figured it would be a fun project for a snowy day. Well I actually have a use for an upcoming project that i could use this for. BUT i need to make it safe first. this amp does not use a power transformer, but is instead a "Hot chassis" unit connected directly to the AC line. not very safe. Apparently these were part of an electronics course i have read! yikes! So digging around it looks like it can be made safe by using a 1:1 isolation transformer. and I have seen some posts of other amps that use a 50C5, 35W4, 12AV6 combo and it appears they connect the isolation transformer as shown in my badly photoshopped schematic. Is this safe? is this the safest way?
Or should I add a center tapped secondary Isolation transformer and a couple of diodes. connecting the CT to ground and the two dioes before the rectifier tube?
Suggestions on how to make this amp safe. Please and Thank you!
ZC
a Couple years ago i picked up this cute little Graymark 509 Amp kit off eBay. I have not had a real use for it but figured it would be a fun project for a snowy day. Well I actually have a use for an upcoming project that i could use this for. BUT i need to make it safe first. this amp does not use a power transformer, but is instead a "Hot chassis" unit connected directly to the AC line. not very safe. Apparently these were part of an electronics course i have read! yikes! So digging around it looks like it can be made safe by using a 1:1 isolation transformer. and I have seen some posts of other amps that use a 50C5, 35W4, 12AV6 combo and it appears they connect the isolation transformer as shown in my badly photoshopped schematic. Is this safe? is this the safest way?
Or should I add a center tapped secondary Isolation transformer and a couple of diodes. connecting the CT to ground and the two dioes before the rectifier tube?
Suggestions on how to make this amp safe. Please and Thank you!
ZC
Attachments
Yes I realized after I sent the post that I meant to have the fuse and switch in the hot leg together
I was just going to connect the heaters to the secondary side of the transformer?
Even in cases where power transformers were used, a series heater string was often used on the non isolated side. That did leave it vulnerable to h-k shorts. If your transformer has 120 volts on its secondary it’s better to isolate. Even if you use a 240VCT and two diodes (to balance the DC flux) you can still connect the heater string to one leg. Just make sure the preamp tube‘s heater is the one tied to ground (unless you like hum).