Supro S6606 build

[sluckey]

Sluckey, Those Keyway replacements look cool but the plate looks to be about 1/8" thick and that loss of insertion into the socket may have a negative effect.

They are less than 1/16" thick. They work just fine.

[Willabe]

Sluckey, Those Keyway replacements look cool but the plate looks to be about 1/8" thick and that loss of insertion into the socket may have a negative effect. I think the actual pin insertion is maybe 1/4" so the pins will be barely connected at 1/8". I'd be more inclined if the top plate was thinner.

Naw, I've used that keyway replacement before. There's still plenty of tube pin sticking up. 

Spending $80.00 on a NOS rectifier is not going to happen. I have a Variac for that.
I don't think I have any voltage issues with a standard Champ PS.

Just making sure you know, not telling you to buy a NOS tube.

Guys post here fairly often that their amp with a 5Y3 rectifier tube is running dcv high, ~30 to 40dcv

A variac can work, as long as it doesn't start dropping the heaters more than 10% down. 

[AnalogDok]

The lowest voltage I use with a Variac is about 79V. Lower than that and you get diminishing returns.

[Willabe]

The lowest voltage I use with a Variac is about 79V. Lower than that and you get diminishing returns.

When you drop the wall acv down to 79v's what acv are the heaters at? 

[AnalogDok]

I never measured voltages with the Variac on.
I have a mega modded Valve Jr with a Fender Tweed style interactive volume/Tone setup that I like to take way down to 79VAC.
It does a really cool brown sound on low voltage. Next time I run it, I'll check.

[Willabe]

Most receiving tube data sheets show +/- 10% for heater voltage, ac/dc. 

So for a 6.3 heater, they can be run anywhere from 5.67ac/dcv to 6.93ac/dcv.

Running them lower or higher than that can/will damage the tube and/or shorten the life of the tube. 

[AnalogDok]

For a 5F1 circuit with modern/cheap/ easy to replace tubes it's no big deal.
For a AB763, it's a different situation all together.

The low heater voltages are less problematic than higher ones AFAIK.

[Willabe]

The low heater voltages are less problematic than higher ones AFAIK.

There your tubes, so you can do what you want.   

With low heater voltage, the cathode doesn't get hot enough to release (enough) electrons and the high dc plate voltage stripes the cathodes coating, destroying the tube. The lower the plate dcv, the less it could be an impact on the cathodes coating. (Certainly not like a transmitting tube with 1000dcv or more.) But the cathodes still not going to like it. And modern tube cathode coatings are probably not as good as NOS tubes.

That's why guys use other ways to lower PSU dcv, because you can only lower the input wall acv so far before you affect the PT's heater wind. Different rectifier tube, higher value B+ series dropping R's, Power Scaling/VVR, combination of a few or several of those including some lowering, but not all from a variac, etc.

[AnalogDok]

So I blame you Willabe...

I went back to my tube charts and verified the 10% margin from 6.3V and looked at my build notes on my 5E3, AB763 and AA1164 and decided to fix them all. The A029 transformers that I used in all 3 builds at my wall voltage of 122.5VAC produce 7.42VAC on the 6.3V filaments and 5.9VAC on the 5V filament. I ordered the correct value resistors to balance the filament lines and drop 1V on both of them.

I should have 4.95V on the 5V rectifier side and 6.4V on the tube filaments. Well within spec and still fine should the voltage go up to 125VAC.

What capped it was when I saw some arcing or sloughing off of material in a brand new JJ GZ34S in my AB763 when I started it up on wall voltage. I shut it down immediately and am waiting for the Dale 5 watt wirewound resistors I ordered from Mouser.
I did the math on all 3 amps for current draw and voltage drop and ordered the appropriate resistance values. I hope I got it right.
These are 1/2 value as I'm pairing them.
For the 5V filaments, AB763/GZ34S = .27Ω x 2, 5E3/5Y3 = .25Ω x 2, AA1164/GZ34S=.27Ω x 2
.15Ω x 2 for all the 6.3V filaments.

I split the values in 1/2 on my calculation and am using a pair of resistors to do the balanced drop.

[Willabe]

Now try your variac.

See how much you have to drop the wall acv to get the heaters where they should be. If it's within 12acv,
then you could build a bucking transformer box. From Sluckey's web site, 2nd page, Buckaroo;

http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

What capped it was when I saw some arcing or sloughing off of material in a brand new JJ GZ34S in my AB763 when I started it up on wall voltage.

That sounds more like too much inrush current from 'hot switching' the rectifier tube with the standby switch.

'Hot switching' is when the rectifier tubes heater is fully warmed up so it can pass current when asked to. In standby mode, the rectifier tubes heater is fully warmed up and so are all the tubes, so when you put the standby into play mode the B+ filter caps and the tubes draw current. (Although the tubes are drawing a lower current at idol, because no ac signal is being applied.)

This can overwhelm the rectifier tube, it can't pass all the current that's being drawn. Once the B+ filter caps are fully charged up, they don't draw as much current just to keep them charged. Then the amps PSU settles into it's normally designed current draw. This takes the extra B+ filter caps inrush charging stress off the rectifier tube which it was not designed/spect to be able to supply.

Do you have the B+ 1st filter cap before the standby and the B+ feed to the OT CT after the standby? If not, when you put the standby in play mode, the B+ filter caps can draw enough current to cause the rectifier tube to arc. 

Should be wired like this;

https://el34world.com/charts/Schematics/files/Fender/Fender_super_reverb_ab763_schem.pdf

[AnalogDok]

The issue was not waiting for the tubes to warm up. You were right.
I resolved the high voltage on the filaments with the resistors to drop the voltage. My 5V is at 4.85 3% and my 6.3 is at 6.12 3% on wall current.

Now I have to check all the voltages and figure out why I have almost no output.
My Bias voltage came down to -39V and the plate voltage is 440V so I set the Bias at 20mA for the moment.

[AnalogDok]

I ordered the keyway plates so I can have some 5Y3S spares. Thanks all for the suggestion and clarification on the thickness.

I also ended up with a 1.5K 5W cathode resistor as I only had 1K and 1.5K in my box. 1K was still too hot.
I'm at 50% with the 1.5K and it sounds really good. It's less noisy and after 6 on the volume I have I have bluesy breakup and more after that.
No farty sound at all and a pleasing single ended amp. It gets plenty loud.
362V Plate and 19.5mA.

The new PT is the same Mfg and part# Weber as the one before. It's just not fried like the last one and it went in just fine.