almost a 6G6 build

[pontiacpete]

I;'m putting together a bass amp using a pair of transformers from the remains of an Earth Sound Research amp. The shell of this ESR amp had 2 X 12" speakers and 4 octal sockets with a SS preamp. I took some measurements of the PT and OT and decided to build a 6G6 with 6L6's and without the normal channel. Its all completed and this is whats going on;

509v of the plates and screens
-53v on the grids
15mA and 17.7mA on the plates..

For the biasing of the grid I lowered the 56K to 22K to bring it from -63v to the -53v. I tried a 6.8k there and brought the voltages on the rail down to 470v , but then one screen resistor ,407ohm, started smoke and red plating when I went to standby((??)) weird.
{BTW there is strange snap when turn off the standby still}

I didn't have 600v caps for the filtering power supply , but ended up with what I have 4 - 20uf/500v and one 20/450v for the first preamp tube.

I figured the OT needs a 16ohm speaker , perhaps in the original ESR amp they used 2 X 12" 8ohm speakers in series, Does anyone have a clue on this?

Also, I'm a little concerned about the 509 or 10 volts on the first cap after the choke, could this be a problem? Should I parallel a resistor(?) with it to protect it .
The first 2 that are paralleled I'm hoping aren't problem, or are they?

And finally, I'm wondering about my layout , cramming it all into this small chassis. Any thoughts?

thanks for any help whatsoever... Happy NEw Yearss

pete

[pontiacpete]

just to follow up on this post that had no takers
I found from a discussion with another person from another forum that running the B+ at about 509vdc would not be good for the pair of 6L6s. Maximum voltage rateings for 6L6GCs is 500v.
These trannies were probably designed for an amp using EL34. There are as I said 4 octals sockets in the original cab they came from.
It was suggested that I bring down the B+ by about 40 volts. There's these zener diodes that weber sells at $20 a pop that can be put on the top of the bridge rectifier or 2 of them on either end of the HV winding.
Then there's this other method that someone suggested, to put a small transformer in series with one on the HV windings and luckily enough I happened to have a $3 transformer that, after some tests,brought the voltage down to 464v. So I'm going with that and hope that it works. If it doesn't I'll just have to spring for a more appropriate PT.

The OT transformer is actually an 8 ohm transformer not 16 ohms
.

[afm_380]

You can get Reverse Polarity Zener Diodes for about $6 a pop from places like Mouser Electronics.
But, I'd be tempted to modify the power tube sockets to accept the EL34's (here's a link that explains the mod). With the zener in place with the flip of a switch you could run EL34's or 6L6's

[pontiacpete]

thanks afm!

that looks to be the same as what weber is selling.

[tubeswell]

Hi Pete

Alternatively, you can just use a string of 5W zeners in series of the High Voltage secondary CT. (Works for me)

Cheers

[pontiacpete]

Thanks Tubeswell, that's another good idea. Ive got to get some higher watt zeners, higher than what I have now,1 watt, to experiment with to see what is easier to fit into my present layout.
I'm also interested in hearing what this amp sounds like with EL34's as AGN suggested.

[tubeswell]

If you have 5W axials you can easily put several of them in series (between the CT and the ground return) to get close to the desired voltage drop.

e.g.; 9V + 12V, or 15V + 15V etc. The power rating adds up this way. and go can add heat sinks on the leads to improve their power dissipation. Banded-end(s) points to ground.