ODS plate resistors and cathod bypass caps

[flatart]

I'm building a ODS 50W clone and I would like to know if someone of you have already experimented with following different solutions:

- preamp plate resistors should be 100K. However many of the later amps with the Skyliner EQ have 220K plate resistors on the preamp tubes.

- The clean stage has 10uf bypass caps across the cathode resistors, while many of the other ODS amps had 5uf capacitors.

a feedback on this would be really appreciated
thanks

[Structo]

What schematic or laypout are you following?

The Ceriatone 50 w OTS is a pretty good representation.

[Fischerman]

The larger plate resistors also use larger cathode resistors. With the larger cathode resistors you would use a smaller bypass cap to get the same frequency response as a 100k plate/1500 ohm cathode. I think the 100K plate/1500 ohm cathode combo typically gets a 22uF bypass cap. But the 220K plate/3300 cathode combo typically gets the 5uF bypass cap...and then sometimes people use a 10uF or a 1uF on one triode just for tone tweeks.

[flatart]

thanks Fischerman.
From your answer I understand that there are not great sound differences, because "200k - 3.3k - 5uF" solution (plate, cathode res, cathode cap) has more or less the same frequency response of "100k - 1.5k - 10u".
Right?

[Structo]

It does change the tone a bit, I went from the stock 180K/120k plates to 220K/150K on both V1 and V2 with the 2K2/3K3 cathodes and 5uf on all but V1b which is 10uf. It knocked down the bass on OD a bit.

[Fischerman]

I don't calculate it flatart but it's not hard to do. I'm more of a 'send it up the flagpole and see who salutes' kind a builder...I just plug it in and listen.

But I'm pretty sure I've read dogears say that the 100K plate amps always or almost always had 25uF bypass caps. I think 5uF is sort of the default value for high plate amps but people sometimes use one of the other values (10uF or 1uF) on one of the triodes (like Structo did above...he used 10uF on V1b).

My suggestion: If you build a 100K plate amp then use use 25uF and if you build a high-plate amp use 5uF. Play the amp get to know it...then try a few different values and see what you like.

[Structo]

#124 had 100K plate loads and used 10uf on V1 and used 4.7uf on V2.

[flatart]

In fact the best way is to experiment and for sure it's what I will do. I will start with #124 base schematics and I will buy some other resistors and caps just to try which combination sounds best

[Structo]

I changed my D'Lite to the higher plates, 220K/150K and the 3k3/2k2 cathode bypass and that made a pretty good change for the good.

I also have the 120K/110 plates on the PI, 4.7K feedback resistor and 150K FET resistor.

The Power tubes have 470R screens and 3K3 grids.

The choke resistor is 330R.

I also installed dual bias pots for the power tubes.

[JamesO]

Tom, what would you characterize the different between low plates and high plates? I thought it was a frequency thing (having not tried it). Is it a feel thing?

[dogears]

The grail 100K plate amp I saw had 25uf on V1 and 5uf on V2.

124 had 10uf on V1.

I think the point is that the low plate amps sound great with something bigger than 5uf. Makes sense.

[Structo]

Tom, what would you characterize the different between low plates and high plates? I thought it was a frequency thing (having not tried it). Is it a feel thing?

It's hard for me to compare the two since I changed the preamp tube resistors and caps quite a while ago but I would say on the D'Lite it takes it more towards the Dumble tone.
I think the PI plates at 120K/110K made a big difference as well as going to the high plates on the preamp.
It was not very single coil friendly in the stock config.

And while it still seems to like my humbucker guitars better, the strat and tele sound better as well now.

I think with the D'lite it was geared more towards the 6V6 tubes and as such it still sounds great.
I never tried the 6V6 tubes as I had ordered the D 44 kit with 6L6 tubes.

When I first built it my amp had too much bass which was on the loose side. I had originally had the bass pot jumpered what some call the bass mod. That was among the first things I changed in trying to get rid of the flabby bass. I want to try to connect that to the PAB relay so it is jumpered when PAB is off and disconnect when PAB is on.


So I can't really compare the two or the differences.

I pretty much have all the changes that Scott has recommended and the ones that are shown on the Tweeked layout.

It is a great amp that I will enjoy for years.