Relay Power?

[raveonstevie]

My amp is a Fender Princeton Reverb II, from the 80s. It runs four 12AX7s and two 6V6s. All heaters are powered by the stock PT.

I had a guy do some work seven years ago and he added relays and switching. He also added a new transformer for relay power, which is in the way of installing the chassis into the cabinet properly. He put it in the only open space, but it is in the way.

I have a two button footswitch; I’ll be switching two relays, possibly three at the most.

I’m seeking opinions on the safety of the original PT. Does adding the switching for two relays, possibly three, require a separate 13v transformer?

Also, another socket for a fifth 12ax7 Was installed, but it is not being used yet. What if I use another 12ax7 later on?

[raveonstevie]

Next question is, he has the low side of the DC relay power going to ground. I guess I should change that? Thanks

[T Wilcox]

Hi, check out Hoffman amps site for relay boards and wiring diagrams to use your existing 6.3vac for switching.
This is for 5vdc relay.. Is your relay 12vdc coil now?
I used his power board and 4 relay boards for a 3 channel switcher recently with great success
Not sure what you mean by "low side of dc relay power"?
If the existing switching already works good can you move/relocate the tranny? That would be the easy fix

[pompeiisneaks]

You could do the math on how much the current tubes use, and how much that transformer can support... I think, though, that often having a separate winding/transformer than the heaters is wise because it reduces the chance of switching noise coupling into the tubes via the heater lines? Maybe not, but it seems possible to me at any rate.

~Phil

[dorrisant]

Your relays can most likely be ran from your filament supply. Also, that PT should handle the extra capacity required for the extra 12AX7.

Your info says Southern Indiana, how close are you to Evansville?

[raveonstevie]

Hi, check out Hoffman amps site for relay boards and wiring diagrams to use your existing 6.3vac for switching.
This is for 5vdc relay.. Is your relay 12vdc coil now?
I used his power board and 4 relay boards for a 3 channel switcher recently with great success
Not sure what you mean by "low side of dc relay power"?
If the existing switching already works good can you move/relocate the tranny? That would be the easy fix

My relays are 5v, but the transformer installed is 13v. It’s working fine but there is no other place under the chassis to put it. When I go to put the chassis in the cab the trans bumps the speaker baffle and won’t go in all the way.

The guy who worked on it called me and had me measure to see if it would fit. I guess he thought I was wrong when I told him it wouldn’t fit. He just knew it would fit because all those “old Fenders” are the same. I tried explaining several times that this amp isn’t one of the classics but I didn’t seem to come across. I’m not mad. You get what you pay for. This was done in 2013.

I have a new transformer one of you guys recommended from Mouser on the way. It is 6.3 volts and should fit.

[raveonstevie]

You could do the math on how much the current tubes use, and how much that transformer can support... I think, though, that often having a separate winding/transformer than the heaters is wise because it reduces the chance of switching noise coupling into the tubes via the heater lines? Maybe not, but it seems possible to me at any rate.

~Phil

Yeah, I have an extra tube slot I’m not sure what to do with so I have another trans on the way. It’s 6.3 volts and will fit. Better safe than sorry and less chance of noise I guess.

[raveonstevie]

Hi, check out Hoffman amps site for relay boards and wiring diagrams to use your existing 6.3vac for switching.
This is for 5vdc relay.. Is your relay 12vdc coil now?
I used his power board and 4 relay boards for a 3 channel switcher recently with great success
Not sure what you mean by "low side of dc relay power"?
If the existing switching already works good can you move/relocate the tranny? That would be the easy fix

The negative terminals of bridge and VR are grounded to chassis. Thought it was supposed to float. Didn’t know what to call it. I’ll probably change that. It works fine though.

[raveonstevie]

Your relays can most likely be ran from your filament supply. Also, that PT should handle the extra capacity required for the extra 12AX7.

Your info says Southern Indiana, how close are you to Evansville?

I’ll try to PM you.

[martin manning]

I have a new transformer one of you guys recommended from Mouser on the way. It is 5 volts and should fit.

You have a bridge rectifier that will drop about 1.4V, and a 3-pin regulator that needs as much as 2V of headroom. I think you need a transformer with at least a 6.3VAC secondary to make this work.

[raveonstevie]

I have a new transformer one of you guys recommended from Mouser on the way. It is 5 volts and should fit.

You have a bridge rectifier that will drop about 1.4V, and a 3-pin regulator that needs as much as 2V of headroom. I think you need a transformer with at least a 6.3VAC secondary to make this work.

I meant 6.3 volts. It’s one that one of you recommended. I think it will work. I’ll fix my post.

[raveonstevie]

http://www.stratopastor.org.uk/strato/a ... #schematic

[url] http://www.stratopastor.org.uk/strato/a ... #schematic[\url]

That is the schematic for what my amp used to be. I removed the reverb, tank and all. The preamp and overdrive are very close to the original “70s Dumble” online schematic. I also added Merlin’s one 12ax7 effects loop.

I don’t fully understand impedance and loading. The amp sounds great but I had a little trouble matching volumes between clean and overdrive. Seems like overdrive volume can drop when using PAB. That make any sense?

I have one preamp tube spot and the reverb transformer available for use. I tried running the overdrive of off the reverb trans but it changed the tone a lot and I don’t really feel like tweaking it. There was also some noise coming off the trans.

Would a 12at7 cathode follower between the tone stack and overdrive be useful for impedance/loading? Would a 12at7 buffer be useful? More gain? Any ideas what I can do with the tube slot and trans?

Thanks for the replies.

[T Wilcox]

Just noticed you are going to try to replace the existing 13 volt trannie with a 6.3v....
You realize the rectifier power board components will have to be changed as well to take that 6.3vac to 5vdc.
Its only a few components but it will be necessary
Heres a link with all the info you should need https://el34world.com/projects/relay_switch.htm

Good luck

Todd

[raveonstevie]

Just noticed you are going to try to replace the existing 13 volt trannie with a 6.3v....
You realize the rectifier power board components will have to be changed as well to take that 6.3vac to 5vdc.
Its only a few components but it will be necessary
Heres a link with all the info you should need https://el34world.com/projects/relay_switch.htm

Good luck
By
Todd

Thanks for the reply. My VR is a 7805. Apparently it can regulate more than the 7.5 volts it’s rated for. My relays are switching fine. My capacitor is 1000 uf, 25 volts. I see Hoffman’s board uses a 4700 uf. Might have to change that too. There’s also a 100 uf, 100v electrolytic with negative to chassis and positive to the negative terminal of regulator.

I now have 16 volts ac going to bridge, 15 dc out, 5 v dc coming off of center lug of regulator.

6.3 volt, smaller in size transformer gets here tomorrow. Will be nice to fit chassis into cab properly.

[dorrisant]

No need to change that cap if the relays are working fine.

Also, if in not mistaken, the regulator's center leg is grounded. Left leg is input. Right leg is output.

Right?