New AB673 deluxe reverb combo build

[sluckey]

Ok pretty well all done but I have a problem My voltages at the output tube plates is way high at 470 volts. Also if I try raising bias higher than about - 50 volts I start getting redplating in both 6v6's

467VDC is the theoretical maximum no-load voltage you can get from that 330-0-330 PT. If you really have -50v on pin 5 then those 6V6s would be barely conducting. Once the power tubes are pulling current that voltage will drop. Redplating does not fit with the voltages you have posted. I suspect you may be a bit confused about something here. What indication do you have that the tubes are redplating? Can you post a pic showing the redplating?

[aussietim]

Went through the measurements again today and got different results the biggest difference is I used a 8ohm 100watt resistor instead of the speaker
One of the reasons that I stopped yesterday (aside from the power tubes glowing bright red and giving off heat like an electric radiator), was the high pitched squeal coming through the speaker when I tried to set bias voltage to -35 volts from - 65volts.
My intention today was to get to the -35 volt mark then photograph the glowing tubes then turn it off so that I had a photo of the tubes glowing to post for you guys, but with the dummy load I got to -35 volts without the power tubes glowing
On B1 I got 480 volts in standby and 465 with everything on
The Plate on V1 was 195 volts V1cathode 1.63 v
Plate Voltage on V 7 & 8 was 466 volts
Heater voltages 6.5 v at the power tube end and 6.45 at the v1 end
Could I have a faulty speaker?
Still seems to me to be high power tube voltage, is it as simple as putting in another rectifier valve as Martin suggests?
Do I need to do some maths and stick a resistor somewhere to reduce the voltage?
To my brain having built a stock standard amp I should be able to use the standard Rectifier
Thank you in advance
Tim

[sluckey]

Remove the dummy load and reconnect the speaker. You need to hear what's going on. The squeal probably means a NFB phase reversal which is common on a new build. Disconnect the NFB wire from the speaker jack. If the squeal goes away then swap the OT brown and blue primary plate leads. Then reconnect the NFB wire.

[aussietim]

Thank you Steve It is the middle of the night here so Ill give that a go in the morning

[aussietim]

Thanks Steve that seems to have fixed it, the Voltage has come down to 426volts. I don't fully understand what happened, so for now Ill just go with it, and do a lot more reading up on it. I have to chase the filthy lucre for the next couple of days, so this will have to wait till then to do more measurements bias adjustments etc but feeling happier now

[martin manning]

I ended up at ~395 using a 5U4, I'd probably be at 420+ with a 5AR4. My unloaded voltage (with only the rectifier installed) was around 490.

There is no reason that anyone should get the primary reversed unless there is a wire color or diagram error. The documentation shows the phasing, or, lacking that you can easily figure it out. The Blue and Brown on the Hammond I used did not match the old Fender layout, but the phase info on the data sheet told me that so I could connect it properly.

[aussietim]

All finished still need to check final bias Sounds really nice
Thank you guys for your help
Trying to work out what to build next maybe a Princeton reverb but like the idea of a Dumble or Vox based amp what recommendations do you guys have for Dumble style builds who makes good boards to base it on?

[aussietim]

PXL_20231006_120153066.MP.jpg

PXL_20231006_120153066.MP.jpg

[martin manning]

Looks nice! Where did your plate voltage end up?

[aussietim]

426 volts
The output transformer must have been wired wrongly during manufacture as when the wires were swapped it started working properly
Thank you for your advice along the way I may or may not modify it later depending on how I get along with it, but for now I am very happy with the noise it makes

[aussietim]

I have a hum when I engage the Reverb not the end of the world but something I would like to try and reduce.
I am thinking of swapping the cabling from the v4 coupling capacitor and the reverb attenuation point to the reverb potentiometer for shielded cables, would this help?
Robrob suggests a .002 uf capacitor on the reverb pedal RCA socket but this seems more for noise and oscillation than humming
Would shielding the reverb pan help?
Apart from the reverb issue the amp is a bit bright but I will see if this settles down as it breaks in before I make any changes

[martin manning]

Is the return end of the tank on the opposite side of the cab from the PT? If not it can pick up 60Hz hum.