SSS - Help

[kaj]

Hi
I need help with a SSS build. I`m building using the "nr.2 schematic"
My problem is the bias voltage, I have apx. -63V at biaspoint, then -36v on the other end of the 220Kresistors. This end of the resistors are connected to the 1,5K gridstoppers on the 6L6 tubes and pin 3+8 on the tube after the PI (the spec SSS tube). That looks nice until I put in this tube, then the bias voltage raises to -4V ! Not good! What can I have done wrong??
Another thing. Those triodes are normaly rated for max 300V Ua. Acording to schematic, bouth sides is powered from "E" apx. 435Vdc, and with the full bias voltage of -36V on the catodes, there is a voltage span on apx. 470Vdc over this tube. Can somone explaine how it is suppose to work??

Cheers Kaj

[mhartman]

Can you post the schematic and a pic of your build. Thx.

[kaj]

[quote="mhartman"]Can you post the schematic and a pic of your build. Thx.

I`m not shure you can see the problem on thr pics. But you probaly see that I (partly) used your layout.

[tictac]

One detail that is missed in these SSS schematics is that the 3K3 resistor needs to be about 10W rating to be on the safe side.

I had a 2W rating in my amp and it nearly got toasted... I used two 6.8k 5W in parallel and it worked fine....

TT

[tictac]

Dude, am I hallucinating or do I see BARE copper wiring being used in the vicinity of the power tubes and the highest voltages in the amp?

You are asking for MAJOR trouble both from an electrical and safety standpoint. I hope for your sake it's just an out of focus picture causing an illusion...

If you are using bare copper around the power tubes you should replace with insulated wire and have a more standard lead dress that you have now. Look at other examples of neatly wired 100W amps, Look at the Fender Twin and Showman layouts... etc....

TT

[ToneMerc]

Dude, am I hallucinating or do I see BARE copper wiring being used in the vicinity of the power tubes and the highest voltages in the amp?

TT

It's no optical illusion....wow!

TM

[David Root]

Man, you better fix that wiring before you get electrocuted and/or burned to a crisp!!

[amplifiednation]

It almost looks like plumbing!!! You can even just put heatshrink on those runs

[mhartman]

Did you take your bias from the HT tap or from the bias tap on the power transformer? It should come from one leg of the HT. I couldn't tell from the pics. Cool amp. Clean up the bare copper wire, but otherwise looks like a fun build. I like the boards with the pics.

[ToneMerc]

Looks like that 100pf PI "fizz cap" is on the wrong side of the plate resistors as well.

TM

[vibratoking]

Coat hangers conduct and they're cheap.

[kaj]

Did you take your bias from the HT tap or from the bias tap on the power transformer? It should come from one leg of the HT. I couldn't tell from the pics. Cool amp. Clean up the bare copper wire, but otherwise looks like a fun build. I like the boards with the pics.

Thanks fore your support! All of you. And I realy got some folks attention with me using some enamel copper wire.
Are you gays thinking safety? or microfonic disturbance? The safety issue - it is dangerous sticking your fingers in an amp that is powered up! There are lots of places to be electrocuded, it does not have to be on the enameled copper.
The 100pF was on the HV side of the 100K plate resistors! Thanks for the notis!
Now to my problem, I use a transformer with an 60Vac Biastap, I have apx. -66V at the biaspoint, and -4V on the other side of the 220K reststors, without powertubes installed. If I remove the (PI/CF)tube, I get -37V at the powertube 1,5K gridstoppers. How come???
I would appriciate if you have an opignion about the voltage range over the (PI/CF) tube. (Apx.470Vdc)
BDW. Have a look on my site www.kaox.dk there you can see some of my other 25 amp-builds There are always room fore improvement! So comments from you "experts" are welcom. I build everything my self, and I also often wind the transformers.

Cheers Kaj

[ToneMerc]

Did you take your bias from the HT tap or from the bias tap on the power transformer? It should come from one leg of the HT. I couldn't tell from the pics. Cool amp. Clean up the bare copper wire, but otherwise looks like a fun build. I like the boards with the pics.

Thanks fore your support! All of you. And I realy got some folks attention with me using some enamel copper wire.
Are you gays thinking safety? or microfonic disturbance? The safety issue - it is dangerous sticking your fingers in an amp that is powered up! There are lots of places to be electrocuded, it does not have to be on the enameled copper.
The 100pF was on the HV side of the 100K plate resistors! Thanks for the notis!
Now to my problem, I use a transformer with an 60Vac Biastap, I have apx. -66V at the biaspoint, and -4V on the other side of the 220K reststors, without powertubes installed. If I remove the (PI/CF)tube, I get -37V at the powertube 1,5K gridstoppers. How come???
I would appriciate if you have an opignion about the voltage range over the (PI/CF) tube. (Apx.470Vdc)
BDW. Have a look on my site www.kaox.dk there you can see some of my other 25 amp-builds There are always room fore improvement! So comments from you "experts" are welcom. I build everything my self, and I also often wind the transformers.

Cheers Kaj

Look at the schematic you posted and read what Mhartman said again, it then should be apparent that your bias supply is connected to the wrong location.

TM

[David Root]

I think it is unwise to use enameled wire as hook-up wire in high voltage areas. That is simply asking for trouble. Yes it's a safety issue. I seriously doubt that EU electrical regulations would allow it.

"Enamel" is basically a chemical varnish, maybe a few thousandths of a mm thick, that is easily broken by minimal contact with anything metallic.

Proper hook-up wire insulation is PVC or teflon sheathing and is much thicker and specifically designed for high voltage use. That is why it exists, because enameled wire is just not suitable for that application.

Inside a transformer is a different matter altogether in my mind. Enameled wire there is relatively safe as it is fully enclosed, made immobile in an insulating matrix, and can't be poked at.

Having said that, most of us don't insulate bare component wire eg resistor, cap leads as they are short, maybe a cm or two. EU regulators may have trouble even with that in the future, they seem to be pickier than US regulators in that regard.

[amplifiednation]

You can't use the bias tap with this schematic. The supply should be taken from one side of the Transformer secondary.

The bare copper just gives more places for things to go wrong...like if a tiny sliver of metal or a piece of solder or something was loose inside the amp, it could essentially complete the circuit to the chassis. Nothing worse than troubleshooting what ends up being a "sliver of metal" as you watch a dropping resistor go up in flames and blowing the last 3A fuse you have.