can cap question

[surfsup]

So here's what I did, with some photos...I took out the first cap can with series configuration. I replaced it with two axials twisted and mounted to a new terminal strip on one of the previous mounting holes for the cap can.

This seems to work well, and there is plenty of clearance around those electolytics so it should be fine. I didn't cover the hole.

On the other cap cans, I replaced them and I think I screwed up on the second one - which was just like the original. I didn't have a phenolic plate and I should have pulled one off the other cap cans but this was my first cap can I've ever used and I just mounted it to the chassis. Following the grounds I now have two points where they meet the chassis. At the metal-finish can and at the original spot on a solder ring at a pot on the control face.

I fired it up after replacing all the other electros with new ones, didn't put in tubes yet. Wondering if I will get hum from the capcan at the chassis causing a ground loop.

I get 348 VDC rather than 290 like the schematic shows for the B+, I don't have tubes in so I assume it will drop some. The original supply is 117VAC and mine measures 126.6VAC right now sheesh! I expect this to settle into the upper 300-310 area.

It takes about 3 mins to drain the resevoir caps from 348VDC to ~50VDC. I want to put in a bleeder. On this type of rectifier (voltage doubler), one single 330k from B+ node to ground would be sufficient? Since the resevoir caps are in series, I assume the "top" one will drain through the "lower" one. I will probably put it across one of the tabs on that first 100/100u black JJ cap can.

Any comments appreciated as usual...

[surfsup]

With all tubes in i get 299vdc B+ with wall supply at 124.1vac right now. The filaments are at 6.8v, i am wondering if this should be dropped some since the wall supply goes over 126 around here,

The five tubes are:

2x6CL6 - 650mA x 2 = 1.3A
6CB6 - 300mA
6aw8 - 600mA
12at7 - 300mA

This is 2.5A draw, so to drop 0.5v, i'd want a 0.25R 5w resistor. Since these being older tubes, am I over-reacting?

[tubeswell]

Is that 6.8V the loaded voltage?

Even so, most 6.3V heaters will still work okay at 7V, so try it and see

[surfsup]

Is that 6.8V the loaded voltage?

Yes, all tubes in w/wall supply @124. I've measured higher wall supply as well.

[Structo]

I think 330K is too high for a bleeder resistor.

That would take a long time to drain.

I typically use a 220K.

You can use the R/C formula to calculate time.

[ToneMerc]

With the way you have it configured with only the single bleeder resistor(not dual resistor capacitor balancing) to ground, I would leave the 330K as to not further pull down your B+.

No need to worry so much about RC constant for a bleeder resistor, it just means you wait a few more seconds

TM

[surfsup]

I was planning to use a 330k 1W. I calculated 0.37Watts dissipation bridging 350 V across the resistor. I probably have a 2W though so I might use that. Right now they take 3-4 minutes to drain. The difference in time between 220k/330k is less than it takes to remove one of the chassis screws...

My main concern is the heaters. Doesn't sound like it is a huge issue. Since the tubes in here are rare (for me, I don't have any spares), I might order a couple 0.5R 1% 5W from mouser next order, parallel them, and put it on one leg coming out of the PT down the road anyway. This should put them around 6.3 which would make me happy.

[Firestorm]

I was planning to use a 330k 1W. I calculated 0.37Watts dissipation bridging 350 V across the resistor. I probably have a 2W though so I might use that. Right now they take 3-4 minutes to drain. The difference in time between 220k/330k is less than it takes to remove one of the chassis screws...

My main concern is the heaters. Doesn't sound like it is a huge issue. Since the tubes in here are rare (for me, I don't have any spares), I might order a couple 0.5R 1% 5W from mouser next order, parallel them, and put it on one leg coming out of the PT down the road anyway. This should put them around 6.3 which would make me happy.

Or put a couple of hi-watt diodes back-to-back in the heater string. You'll drop the diode loss. Back-to-back so no rectification.

[Firestorm]

I was planning to use a 330k 1W. I calculated 0.37Watts dissipation bridging 350 V across the resistor. I probably have a 2W though so I might use that. Right now they take 3-4 minutes to drain. The difference in time between 220k/330k is less than it takes to remove one of the chassis screws...

My main concern is the heaters. Doesn't sound like it is a huge issue. Since the tubes in here are rare (for me, I don't have any spares), I might order a couple 0.5R 1% 5W from mouser next order, parallel them, and put it on one leg coming out of the PT down the road anyway. This should put them around 6.3 which would make me happy.

Or put a couple of hi-watt diodes back-to-back in the heater string. You'll drop the diode loss. Back-to-back so no rectification.