Identifying Power Transformer leads for FENDER Amp

[czech-one-2]

Your part is suitable. There are 2 corners labeled AC. The red wires go to those.

The minus corner goes to ground, the plus corner is now your positive high voltage.

Look at the capacitors on your power supply, do they handle 500 VDC? You need 500 V rated caps for the higher +B, the 300 VDC ones no longer do the job for this transformer.
Just isolate the bias taps, you won't use them. Keep the cathode bias, it's gonna self regulate using 6L6's and it'll probably sound great.

Thanks,just to be clear..the plus corner goes to where the the red/yellow center tap wire went, correct? And there's only one corner labeled AC and nothing labeled - on the rectifier. I assume the tab directly opposite the labeled one is also AC? Is there anything else that needs to be done other than wiring the tranny to the bridge rectifier and making sure the filter caps are 500v rated?
I'll end it here for a week or so until I decide if I'm going to tackle this. I think it would sound great with the 6l6's and cathode biased, so I may just go for this.
I already have a 6AQ5 Musicmaster Bass amp that Enzo and crew here helped me de-bug and it sounds great. I bought this one cheap cause its not working so I'm hoping to make it a loud little sucker with the higher voltage and 6L6's.

[jmaf]

Thanks,just to be clear..the plus corner goes to where the the red/yellow center tap wire went, correct? And there's only one corner labeled AC and nothing labeled - on the rectifier. I assume the tab directly opposite the labeled one is also AC? Is there anything else that needs to be done other than wiring the tranny to the bridge rectifier and making sure the filter caps are 500v rated?
I'll end it here for a week or so until I decide if I'm going to tackle this. I think it would sound great with the 6l6's and cathode biased, so I may just go for this.
I already have a 6AQ5 Musicmaster Bass amp that Enzo and crew here helped me de-bug and it sounds great. I bought this one cheap cause its not working so I'm hoping to make it a loud little sucker with the higher voltage and 6L6's.

There's only one AC corner because it's a convention for these bridges, the opposite diagonal one is the other AC corner. There's usually a little wiggly sinusoid mark showing each of the two AC corners. The red wires from the tranny go on the AC pins.

The plus corner goes on the red dot below.



Yeah, make sure the high voltage caps all support the new peak +B voltage, 500 VDC.

Right after the red dot there's a 1K resistor that goes to pin 4 screen grids. For 6L6's you might wanna change that to 470 ohm x 5 watts, it increases the punch.

if all goes well it should sound great with 6L6's.

[jmaf]

PS. The negative end of the rectifier bridge goes where the previous center tap went. Not the + end!

Below, green is where negative goes, red is where positive goes. This is critical, or that capacitor dangling from the board blows up.

[czech-one-2]

Wow, great info! Thanks for the layout clarification Jmaf! This looks do-able now
Got this from another helpful forumite-


Last question [for now]...
Will a fender deluxe reverb output transformer be ok? That's what I have [and plan on using]

[czech-one-2]

PS. The negative end of the rectifier bridge goes where the previous center tap went. Not the + end!

Below, green is where negative goes, red is where positive goes. This is critical, or that capacitor dangling from the board blows up.

[ATTACH=CONFIG]39460[/ATTACH]

Ok, I'm gonna do this! However, if I follow your revised layout, what happens to the two diodes on the original board? The two original red wires went there. Do I just continue the red wires from their lugs on the bridge rectifier to the same location on the board that they originally went?

[Justin Thomas]

Those two original diodes can either be removed, or left in but not connected to anything. Personally I'd take them out, just to avoid confusion. The part you are using is basically the four diodes needed for a full-wave bridge, but already rolled up into one convenient little package. So you're replacing two parts with a single part that does the same job.

One red wire should be going to one of the original diodes, and the other red wire should be going to the other original diode. Is that the case?

Justin

[czech-one-2]

Those two original diodes can either be removed, or left in but not connected to anything. Personally I'd take them out, just to avoid confusion. The part you are using is basically the four diodes needed for a full-wave bridge, but already rolled up into one convenient little package. So you're replacing two parts with a single part that does the same job.

One red wire should be going to one of the original diodes, and the other red wire should be going to the other original diode. Is that the case?

Justin

Yes, thats how its currently wired.
Can I put the red wires in the same location and use 2 jumpers instead of the diodes?
Also, that one location [the red dot on the revised layout] is terrible crowded. Any tips for cramming all that in there? Its not a turret board but the old fender eyelets.

[Justin Thomas]

I'll leave that strategy to more experienced builders, those who may have had to get themselves out of a bind... in theory, you could do almost anything, but without pics, it's hard to tell or conceptualize. Also, knowing exactly where the jumpers would be routed would be a huge help, as far as avoiding hum, buzz, and other noises...

Justin

[czech-one-2]

I'll leave that strategy to more experienced builders, those who may have had to get themselves out of a bind... in theory, you could do almost anything, but without pics, it's hard to tell or conceptualize. Also, knowing exactly where the jumpers would be routed would be a huge help, as far as avoiding hum, buzz, and other noises...

Justin

I'll try to post a pic, but it currently looks exactly like the layout diagram. Here's what I'm wanting to clarify:
The two hi voltage PT wires go to the bridge rectifier and continue from there to their original 2 eyelets on the board. However, we no longer need the two board mounted diodes so I would jumper each eyelet to the [crowded] 'RED Dot' location that Jmaf highlighted.
Sound correct?

[jmaf]

I'll try to post a pic, but it currently looks exactly like the layout diagram. Here's what I'm wanting to clarify:
The two hi voltage PT wires go to the bridge rectifier and continue from there to their original 2 eyelets on the board. However, we no longer need the two board mounted diodes so I would jumper each eyelet to the [crowded] 'RED Dot' location that Jmaf highlighted.
Sound correct?

Here :



The two diodes are gone. The red/yellow wire that used to go to the green spot is gone. This is all there is to it.

Remember : if you don't swap those caps for 500 VDC caps or higher they'll blow up.

[nickb]

There are some issues that concern me about this. The new supply is going to be around 480V so a number of things will be affected that need to be tackled. I haven't done the math fully, so EOE .

(1) The plate and screen dissipation will shoot up. To fix this you will need to decrease the bias current to around 30mA to avoid over dissipating the 6V6's. This can be accomplished by changing the cathode bias resistor to about 750 ohms. Use a 5W.

(2) The output transformer will give a plate to plate load impedance of ~10k ohms. This is higher than ideal for a plate voltage this high but is good in helping to keep the tube power dissipation down. Not a worry.

(3) The power output will increase significantly as the plate voltage swing will increase from about 230Vpk to 410Vpk - that's three times the output power. This could cause the output transformer to saturate at low frequencies. What I don't know is if the driver stage can drive it hard enough to get to that level. If the driver is the limit you might not like the cranked sound. OTOH, you might love it.

(4) The higher output power could damage the speaker.

(5) The supply voltage to the preamp, and in particular the drive stage will shoot up. The half of the 12AX7 that is the driver will be close or over it's maximum plate dissipation. You might consider increasing the 10K supply resistor to 33K 2W.

Addendum:

I see you mentioned using 6L6's. I missed that at first. No worries about cooking them. The cathode resistor will need to be about 680 ohms @ 10W. The idle current will be about 40mA.

The cathode bypass capacitor will need to have a >=63V rating too.

PS: Also, the thermal protector might keep tripping.

[czech-one-2]

Here :

[ATTACH=CONFIG]39479[/ATTACH]

The two diodes are gone. The red/yellow wire that used to go to the green spot is gone. This is all there is to it.

Remember : if you don't swap those caps for 500 VDC caps or higher they'll blow up.

Well, that is just awesome, thanks!

[czech-one-2]

There are some issues that concern me about this. The new supply is going to be around 480V so a number of things will be affected that need to be tackled. I haven't done the math fully, so EOE .

(1) The plate and screen dissipation will shoot up. To fix this you will need to decrease the bias current to around 30mA to avoid over dissipating the 6V6's. This can be accomplished by changing the cathode bias resistor to about 750 ohms. Use a 5W.

(2) The output transformer will give a plate to plate load impedance of ~10k ohms. This is higher than ideal for a plate voltage this high but is good in helping to keep the tube power dissipation down. Not a worry.

(3) The power output will increase significantly as the plate voltage swing will increase from about 230Vpk to 410Vpk - that's three times the output power. This could cause the output transformer to saturate at low frequencies. What I don't know is if the driver stage can drive it hard enough to get to that level. If the driver is the limit you might not like the cranked sound. OTOH, you might love it.

(4) The higher output power could damage the speaker.

(5) The supply voltage to the preamp, and in particular the drive stage will shoot up. The half of the 12AX7 that is the driver will be close or over it's maximum plate dissipation. You might consider increasing the 10K supply resistor to 33K 2W.

Addendum:

I see you mentioned using 6L6's. I missed that at first. No worries about cooking them. The cathode resistor will need to be about 680 ohms @ 10W. The idle current will be about 40mA.

The cathode bypass capacitor will need to have a >=63V rating too.

PS: Also, the thermal protector might keep tripping.

Hey Nickb,thanks for considering the other ramifications.
Regarding # 3] I'll be using a tweed deluxe output transformer. I have no idea how this will sound so we will see
#4] I've got a 100w mckenzie speaker going in this one
#5 I hadn't considered that, something to think about/maybe tweek. Also,before I commit to this, what about the phase inverter transformer? Will this part be stressed at all? If so that might be a deal breaker as these are not easy to find a replacement for.

And the cathode resistor needs to be 10w? I've got a suitable 5w block resistor but would have to source a 10w.

[eschertron]

And the cathode resistor needs to be 10w? I've got a suitable 5w block resistor but would have to source a 10w.

A 680R 5W resistor is going to get toasty at about 85ma dissipation (from P = I^2*R), and from my guesstimation, nickb's 40ma is per tube? You could try the 5W to see how long it lasts but be sure to stand it off from the eyelet board to reduce the risk of fire!

[jmaf]

I always use 10W on cathodes even for EL84 and 6V6. If you only have 5W's you can combine resistors and get more reliability.