Tweedle Dee Deluxe causing arcing in rectifier

[pompeiisneaks]

I had played that thing a lot, and then had it sit for a week or so, plugged it back in and it suddenly started crackling like mad, arcing all over in the rectifier.

I replaced the one I had in there with a 5U4GB noting it could handle the 32uF capacitors better (wondered if they were being taxed by the higher capacitance) and it proceeded to start arcing immediately as well.

What could cause this?  I tested the 6V6's again and they work just fine.  The amp was playing just fine as well, now I don't know what went wrong. 

What would cause the rectifiers to arc almost instantly?  Bad pin connections in the socket?  Bad socket? 

~Phil

[pompeiisneaks]

Oh one other thing I did note the first 4.7k dropper resistor is looking pretty toasty too when I opened it up and was looking. 

~Phil

[tubenit]

Did you replace the toasty resistor?   And was it the "correct" value?

Are there any carbon traces on the rectifier or power tube sockets?  Any hairline cracks in the sockets?

Have you checked measured the volts on the rectifier pins with no tubes in the amp? 

Any strands of wire touching something they shouldn't?

with respect, Tubenit

[MFowler]

I had to replace that 4k7 on my Tweedle Dee to 5w it burnt up prior to that.

It's the screen circuit.

Mark

[John]

If it started this after sitting, instead of while playing, I'd look hard at the socket. Maybe it fractured during cool down?

[Ed_Chambley]

Got a. Couple of diodes to as rectify, eliminate try tube and socket, then see if you have a circuit issue like the dropper,

[mresistor]

Did you have a GZ34 rectifier in it?  New production?

[pompeiisneaks]

Did you replace the toasty resistor?   And was it the "correct" value?

Are there any carbon traces on the rectifier or power tube sockets?  Any hairline cracks in the sockets?

Have you checked measured the volts on the rectifier pins with no tubes in the amp? 

Any strands of wire touching something they shouldn't?

with respect, Tubenit

I've not yet, no I should, I also had Mark below mention I shoudl try a higher wattage one, I may go pick one up.  It's a ceramic socket, I'll look and see for carbon, but I didn't notice any.

I am pretty sure I got good voltages on the pins without it in, but I'll double check.

I don't see any wires doing anything they shouldn't. No.

Thanks,

~Phil

[pompeiisneaks]

I had to replace that 4k7 on my Tweedle Dee to 5w it burnt up prior to that.

It's the screen circuit.

Mark

I'll Run to the local electronics shop and get one and give that a whirl.

~Phil

[pompeiisneaks]

Got a. Couple of diodes to as rectify, eliminate try tube and socket, then see if you have a circuit issue like the dropper,

Yeah I've even been told I may want to hard permanently put in some 1n4007's from pin 7/5 to 4/6 so that it protects it from back arcing, I may do that permanently and put in two more for testing temporarily.

~Phil

[pompeiisneaks]

Did you have a GZ34 rectifier in it?  New production?

I didn't have new production, they were all OS pulls I got at hamfests that tested good, and I didn't have GZ34, I was using 5AR4's as I recall, but I do know that I looked up the datasheet and they don't like more than 20uF if I recall, so that may have been part of it, but the 5U4GB I put in was a good one from the same lot of pulls i had that still tests good (But as I understand it, if it's ever arced consider it toast, as it will continue to arc and get worse and eventually blow no?)

~Phil

[pompeiisneaks]

I re-measured the dropper, I'm going to replace it anyway, but it reads 4.6k I think, in the ballpark and in spec.  I read voltages without a rectifier and I get 390 VAC.

~Phil

[sluckey]

I think you just have bad rectifier tubes. Try another one that you know is good.

Looks like you have a 2 watt metal oxide resistor. Measure the voltage across your 4.7K and do the math. I have a 4.7K 2W CC resistor in my 5E3 and it works just fine. But I did add 470Ω screen resistors. Voltage drop across my 4.7K is 33v. So, 33*33/4700=0.23watts. Voltage drop across the 4.7K in the tweedle dee schematic at TAG is 38.7 and the power calculates to 0.32 watts. Using a 2 watt resistor should be fine. It's OK for power resistors to get hot but they should not discolor.

[mresistor]

On adding safety diodes it would be better to add them pin 7 to 6    and    pin 5 to 4  .

[Ed_Chambley]

Got a. Couple of diodes to as rectify, eliminate try tube and socket, then see if you have a circuit issue like the dropper,

Yeah I've even been told I may want to hard permanently put in some 1n4007's from pin 7/5 to 4/6 so that it protects it from back arcing, I may do that permanently and put in two more for testing temporarily.

~Phil

This is always cheap insurance.


This way the amp will work without the tube.  I am undecided on the "best" connection and would like to know if someone has a particualr reason for doing it different.  Truthfully, I put them to the HT leads and to the Rectifier socket.  I do not even use an additional post.

[sluckey]

This way the amp will work without the tube.  I am undecided on the "best" connection and would like to know if someone has a particualr reason for doing it different.

Those diodes only protect the PT and filter caps in the event that the tube shorts. If the tube fails open, or the filaments burn out, or the tube falls out of the socket there will be no B+. There is no "best" way to connect these diodes. Use any of the unused tube pins you want or mount a terminal strip near the socket.

[Ed_Chambley]

This way the amp will work without the tube.  I am undecided on the "best" connection and would like to know if someone has a particualr reason for doing it different.

Those diodes only protect the PT and filter caps in the event that the tube shorts. If the tube fails open, or the filaments burn out, or the tube falls out of the socket there will be no B+. There is no "best" way to connect these diodes. Use any of the unused tube pins you want or mount a terminal strip near the socket.

I meant by the "best method" is I question voltage increases from a 5Y3 to SS rectification.  In most instances probably not a big issue, but if you are already puching your speaker it could let go with your tube.  Shouldn't you have a spare set of tubes anyway?

[SILVERGUN]

Did you have a GZ34 rectifier in it?  New production?

I didn't have new production, they were all OS pulls I got at hamfests that tested good, and I didn't have GZ34, I was using 5AR4's as I recall, but I do know that I looked up the datasheet and they don't like more than 20uF if I recall, so that may have been part of it, but the 5U4GB I put in was a good one from the same lot of pulls i had that still tests good (But as I understand it, if it's ever arced consider it toast, as it will continue to arc and get worse and eventually blow no?)

~Phil

Tested how?....by you? ...or are you just believing the fine gentleman from Hamfest?
Wasn't there an arc'ing incident in one of your videos. I don't remember hearing you explain it, but I do remember a moment where the video zoomed in on it in an "instant replay"
Was that video from this amp build?
What was the outcome of that?
Have you tested for shorts?


At about 2:20 in video 11 it appeared as though you may have created the short with your meter probe?