My #124 88 skyliner( clean only ) comes to life this evening

[bluescaster]

Hi, it's ok, after one week of wiring my #124 is living. It's really the clean tone i was looking for ! I'll put photos and shematics this week-end.

I just build clean channel 50w Dumble ODS (2x5881), i never like overdrive (play SRV, Hendrix, P Sayce, J Mayer...). I use Weber transformer for Super Reverb.

I got 450v before and after the choke, 439v for PI trimmer center tape, 382v for overdrive channel (not wiring), 378v for Clean channel.

247v and 256v on clean channel plates. Very high no ? Perhaps i need to adjust the 22k resistor or put one to simulate overdrive channel load ?

292v on PI plates.

Bias: 443v on 5881 plates. I can't get less than -41v on bias trimm. I put 1r resistor between 8 pin and ground and find 70ma and 62 ma. Very high too, what to do ?

I would like to had something to protect my OT if i forget to plug HP on output. What to do please ?

Kind regards and thank you for all the informations i got on Amp Garage. And thank you Mr Dumble !

[mauiboy81]

What values do you have in your bias supply? Adjust the value of the resistor off the trim pot to ground.
I think on my 2 6l6 clean only I have 50v supply with 2k2 dropping, 10k pot, and 47k to ground. It's what I had available and works perfectly. With 500v on the plates the tubes are at 34ma with room to go.

[bluescaster]

Hi, if i want 35ma current i need to decrease Ubias. If i replace my 27k resistor to 10k, it will increase no ?

[mauiboy81]

Yeah, I got mixed up when I looked at a different schematic. You can just raise it to get where you need to go.

[bluescaster]

Quote: Weber use 470R, 50K pot and 27k.

[ToneMerc]

Hi, if i want 35ma current i need to decrease Ubias. If i replace my 27k resistor to 10k, it will increase no ?

Yes, try that.

TM

[bluescaster]

Hi, #124 use 3k3, 10K pot and 27K resistors. I change 3k3 to 1k and i can get 34ma now but with pot on max. I'm gonna change it to 470 like Fender and i hope this will be fine.

Kind Regards.

[mauiboy81]

Raising the 27k will get you there as well

[CHIP]

You also should bring those clean plate voltages down about 50v.

[dcribbs1412]

Hi, it's ok, after one week of wiring my #124 is living. It's really the clean tone i was looking for ! I'll put photos and shematics this week-end.

I just build clean channel 50w Dumble ODS (2x5881), i never like overdrive (play SRV, Hendrix, P Sayce, J Mayer...). I use Weber transformer for Super Reverb.

I got 450v before and after the choke, 439v for PI trimmer center tape, 382v for overdrive channel (not wiring), 378v for Clean channel.

247v and 256v on clean channel plates. Very high no ? Perhaps i need to adjust the 22k resistor or put one to simulate overdrive channel load ?

292v on PI plates.

Bias: 443v on 5881 plates. I can't get less than -41v on bias trimm. I put 1r resistor between 8 pin and ground and find 70ma and 62 ma. Very high too, what to do ?

I would like to had something to protect my OT if i forget to plug HP on output. What to do please ?

Kind regards and thank you for all the informations i got on Amp Garage. And thank you Mr Dumble !

Sounds interesting...I am in the middle of a 100 watt similar build
would love to see some pics and your schem.

Thanks
Darin

[Structo]

You also should bring those clean plate voltages down about 50v.

I agree.

Your PI voltages are good, but you want around 190-200v max on V1 plates.

I know when we build a ODS amp and don't have the FET circuit loaded that you put a 150K-220K resistor at the end of the dropping string to ground to simulate that load.
So perhaps you need to do the same only a bit more to bring your V1 plates down.

You know you can still install a V2 (the overdrive channel) but you can set it pretty clean and it could be a volume booster or solo boost, that way your power supply would be loaded correctly.

But if you only have V1, the PI and power amp, you only need four power nodes.
Power tube plates B+1, screens B+2, PI plates B+3 and V1 plates B+4.

Do you have a 2K2 before the PI?

Then a 22K?

Try a 220K at the end from the + to ground. (make it at least 3w)

[bluescaster]

I put a 100K to the ground to simmulate overdrive channel load, but have 220v. I will had overdrive channel this week. I'm lust listening Gregor Hilden (red on blue album) that play on an ODS and his overdrive is wonderfull.

[Structo]

Well yeah, that is why most build the ODS, for the overdrive.

[heisthl]

up the 22k to 27k - keep your 100k bleeder (on the node for V1) - should give you 200volts.

[bluescaster]

Hi, i would like to had cathode follower after my PI like this:

[img2924]http://ampgarage.com/forum/files/cf_181.jpg[/img]

My problem is that ECC81 has Ukfmax=80v. How to elevate the heater on the ECC81 ? Did i need a seconder transformer ( and how to do it) or replace the ECC81 with a ECC83 (Ukfmax=180v but is it ok) ?

There is an other solution, but i don't know if it's really ok. if a use a stage like v1b but with 1M in place of 220k and one 1M in the loop, i will get a amplifier factor of -1, 1M input impedance and low output one. Is someone try this yet ?


Thank you