Solved: 1967 Fender Deluxe Reverb, Rectifier Valve Arcing

[Pete Farrington]

I’m really pleased it’s worked out ok, we’re lucky to have Luke to call on. Good idea to tweak the primary for 120V

 

[Spanngitter]

Please confirm secondary HT Wiring resistance Rsec/Rt is within GZ34 specification, if not add some 47 or 100 Ohm Resistor in serie to each HT.
Usually nearly all modern transformers are too low in Rsec/Rt and this will cause your GZ34 suffer (again) a premature death....

 

[Richard Neill]

Please confirm secondary HT Wiring resistance Rsec/Rt is within GZ34 specification, if not add some 47 or 100 Ohm Resistor in serie to each HT.
Usually nearly all modern transformers are too low in Rsec/Rt and this will cause your GZ34 suffer (again) a premature death....

Please confirm secondary HT Wiring resistance Rsec/Rt is within GZ34 specification, if not add some 47 or 100 Ohm Resistor in serie to each HT.

You're killing me, can you not just say great, it works and give my small brain a rest?! 🤣
Can you spell out which wires I should be measuring the resistance between and what value should be expected? Also, will I have to desolder all the wires again to check or can in be done in situ?

Here's the pic of the transformer value wires.



Thanks for pointing this out.

 

[Pete Farrington]

Red to red resistance. Hopefully about 120R or more.

 

[Spanngitter]

You're killing me, can you not just say great, it works and give my small brain a rest?! 🤣
Can you spell out which wires I should be measuring the resistance between and what value should be expected? Also, will I have to desolder all the wires again to check or can in be done in situ?

Nope 👹

Disconnect Amp from Power Outlet, remove the GZ34 and measure between both red cables and then repeat the same from each red to red/yellow (CT, might be soldered to chassis). As @Pete Farrington already mentioned, let's hope that you measure something >120 Ohms in general....

 

[Richard Neill]

Nope 👹

Disconnect Amp from Power Outlet, remove the GZ34 and measure between both red cables and then repeat the same from each red to red/yellow (CT, might be soldered to chassis). As @Pete Farrington already mentioned, let's hope that you measure something >120 Ohms in general....

Right the results are in!

Red to red - 115.3 ohms
Red 1 to red/yellow - 58.9ohms
Red 2 to red/yellow - 56.8ohms

Desoldered
Red 1 to red/yellow - 59.5 ohms
Red 2 to red/yellow - 57.5 ohms

Good/bad or ugly?

 

[Spanngitter]

It barely missed the LCL….with the usual 420Vdc in a Deluxe Reverb you should have >120 Ohms, better 140 as per the chart I posted above. So I would recommend to add a 22R or 33R / 3W to each side when approaching the GZ34 Socket

 

[Richard Neill]

It barely missed the LCL….with the usual 420Vdc in a Deluxe Reverb you should have >120 Ohms, better 140 as per the chart I posted above. So I would recommend to add a 22R or 33R / 3W to each side when approaching the GZ34 Socket

Plate voltage is currently 432v. Will that change anything in regards to what resistors to add and am I simply soldering the resistor from one end of the ht wire to the pin or soldering them between pins on the socket and if so which pins?

Apologies for all the questions and thanks for your patience. I'm comfortable changing parts not so comfortable modding or adding stuff!

 

[Spanngitter]

Do it like this, just with a 22R instead of the 100R (you can also use 100R to ease the life of the 6V6s but it will add more sag as overall B+ drops)

 

[Richard Neill]

Do it like this, just with a 22R instead of the 100R (you can also use 100R to ease the life of the 6V6s but it will add more sag as overall B+ drops)

View attachment 120201

You're a kind soul, thanks again. I take it I ignore the fuse?

 

[Spanngitter]

You can ignore it or add it as normally AB763 Circuit and its variatons do not have an HT Fuse

 

[chocol8]

While you are in there soldering, I would add a couple rectifier backup diodes. They won't impact the tone at all but can extend the life of the rectifier tube and protect expensive parts if the rectifier tube fails.

 

[Richard Neill]

While you are in there soldering, I would add a couple rectifier backup diodes. They won't impact the tone at all but can extend the life of the rectifier tube and protect expensive parts if the rectifier tube

Would I solder the diodes after the resistors or before or does it make no difference? Also, ok to use IN4007s as I have a couple of them lying about.

 

[Pete Farrington]

1N4007 are fine, but ideally use them in series pairs.
Such series diodes are really beneficial, as they seem to stop arcs forming and then wrecking the valve and caps.

 

[Richard Neill]

1N4007 are fine, but ideally use them in series pairs.
Such series diodes are really beneficial, as they seem to stop arcs forming and then wrecking the valve and caps.

I remember you mentioning this earlier in the thread and I looked at the diagram. It seems to suggest just putting a diode on each ht lead, is that right? Would I put that before or after the resistor I'm adding or does it make no difference?

 

[chocol8]

I would put the resistor first and then a diode with the stripe towards the tube. Pete is saying to use two diodes in series on each lead.

 

[Richard Neill]

I would put the resistor first and then a diode with the stripe towards the tube. Pete is saying to use two diodes in series on each lead.

Perfect, thanks folks.

 

[chocol8]

Perfect, thanks folks.

Sorry I had to cut my last answer short due to a call. Pete is saying to use 2 because the peak voltage with a startup spike could exceed the 1000v PIV rating of one. Fender uses a 1500 volt rated diode on newer builds, but if you already have 4 of the 1N4007's, just use a pair in series for the extra protection.

 

[Richard Neill]

Sorry I had to cut my last answer short due to a call. Pete is saying to use 2 because the peak voltage with a startup spike could exceed the 1000v PIV rating of one. Fender uses a 1500 volt rated diode on newer builds, but if you already have 4 of the 1N4007's, just use a pair in series for the extra protection.

I'm waiting on the resistors to arrive then I'll do the lot. I'll pop up some pics when I'm done to make sure it's right. Cheers.

 

[Richard Neill]

1N4007 are fine, but ideally use them in series pairs.
Such series diodes are really beneficial, as they seem to stop arcs forming and then wrecking the valve and caps.

Planning on fixing this today, the resistors have taken quite some time to arrive and I seem to have misplaced my 1n4007 diodes. Can I use 1n5408 in series instead?