#102 Build started

[Ang3lus]

3:

[Ang3lus]

Choke done

[Ang3lus]

power section done except heaters and 2 bias points

[Ang3lus]

what's left:

1. Drilling output transformer holes (using a different one, using a classictone transformer)
2. fitting preamp board and wiring everything
3. fitting power board and wiring
4. wiring output transformer
5. wiring power transformer
6. heaters
7. intial power up

hopefully i will be done in a month or two

[Kassie]

3:

Nice clean work, but I would wire those wires a little shorter.

But indeed never too tight though...

Edit: ohh those are for the relay boards and still to be connected? I haven't said anything...

[Ang3lus]

Finished the amp !!!!

It works great with channel 1, channel 2 (OD chan) I get low volume, all controls are responsive, it's just that the volume is low (max volume is like a 1W amp),

Running 4XEL34

my voltages seem to be too high I think thuogh,

with string droppers at 2k2, 22k I get

B+1 482v
B+2 481v
b+3 473v
b+4 352v
b+5 343v

Anodes:

V1A 224V
V2A 211V
V2A 227V
V2B 219V
V3A 326.8v
V3B 327V

are these voltages ok ?

[ToneMerc]

Finished the amp !!!!

It works great with channel 1, channel 2 (OD chan) I get low volume, all controls are responsive, it's just that the volume is low (max volume is like a 1W amp),

Running 4XEL34

my voltages seem to be too high I think thuogh,

with string droppers at 2k2, 22k I get

B+1 482v
B+2 481v
b+3 473v
b+4 352v
b+5 343v

Anodes:

V1A 224V
V2A 211V
V2A 227V
V2B 219V
V3A 326.8v
V3B 327V

are these voltages ok ?

About 30v high all the way across, but do you have the FET board connected to B5? If not, B3 thru B5 will be about 25v or so too high.

TM

[Ang3lus]

I do have the FET board connected and biased.

I'm using custom speced transformers, the guy who wounded them did all the winds +5%.

[ToneMerc]

I would increase the first resistor to knock down v3 thru v1.

TM

[Structo]

I'll be interested in what you think about the tone with those carbon comp resistors.

Dumble used the RN65 mil spec metal film resistors for most all plate loads starting with the early ODS amps.

Most of us stick to the Dumble recipe but that doesn't mean you can't experiment with different materials to see what they sound like.

This is just a guess but I think that a lot of those surplus PIO caps (Russian?) are leaky and therefore affect the tone.

Also, the 1 ohm bias resistors should be very low tolerance, 1% or less for biasing accuracy.

As far as the OD volume goes, where do you have the OD trimmer set in relation to ground?

[Ang3lus]

That worked

Played around with it, 10k almost did the trick.

now i get

B+3 411v
b+4 306v
b+5 294v

V1A 192v
V1b 181V
V2A 196V
V2b 188V
V3A 283v
V3b 284v

I guess reducing it to 8.2k will be better, will go to the shop next week, no time this weekend.

meanwhile, I have two last problems.

1) OD chan is very low volume, like a 0.5w tube amp, when i switch back to the clean channel i get a siren sound when i turn the overdrive knob back and forth which changes with the travel of the pot. anyone ever exeprienced such a thing ?

2) my 6.3v CT (I have one in my transformer) If i connect it to a GND point, the heaters are shorting to GND (checked that with a multimeter when amp was off, didn't have the guts to fire it up when heaters are shorting to GND), is the CT damaged or is that normal ?

[ToneMerc]

That worked

Played around with it, 10k almost did the trick.

now i get

B+3 411v
b+4 306v
b+5 294v

V1A 192v
V1b 181V
V2A 196V
V2b 188V
V3A 283v
V3b 284v

I guess reducing it to 8.2k will be better, will go to the shop next week, no time this weekend.

meanwhile, I have two last problems.

1) OD chan is very low volume, like a 0.5w tube amp, when i switch back to the clean channel i get a siren sound when i turn the overdrive knob back and forth which changes with the travel of the pot. anyone ever exeprienced such a thing ?

2) my 6.3v CT (I have one in my transformer) If i connect it to a GND point, the heaters are shorting to GND (checked that with a multimeter when amp was off, didn't have the guts to fire it up when heaters are shorting to GND), is the CT damaged or is that normal ?

string: you can leave it and just roll a preamp tubes through

2) normal.....think about it, the center of the filament winding is connected to ground. I always do a continuity check on the filament string, while verifying it is not shorted to the chassis before it is terminated to the power transformer.

TM

[Ang3lus]

I'll be interested in what you think about the tone with those carbon comp resistors.

Dumble used the RN65 mil spec metal film resistors for most all plate loads starting with the early ODS amps.

Most of us stick to the Dumble recipe but that doesn't mean you can't experiment with different materials to see what they sound like.

This is just a guess but I think that a lot of those surplus PIO caps (Russian?) are leaky and therefore affect the tone.

Also, the 1 ohm bias resistors should be very low tolerance, 1% or less for biasing accuracy.

As far as the OD volume goes, where do you have the OD trimmer set in relation to ground?

Clean wise the tone is very good, VERY dynamic and EXTREMELY transparent, switching between pickups there is a very noticeable difference if they are not set right (height wise etc). this is the most sensitive amp i've ever tried.

I used the carbon comp resistors mainly because I had a SLO build with all mil-spec rn65 which sounded so-so, then i built a bogner clone with carbon comp and it sounds AWESOME, so decided to do the same with the dumble.

I'm not after Dumble's tone per se, only after great tone, and this amp seems like a step towards it.

I put the OD trimmer on the front panel on a pot, and i will adjust it as is.

[Ang3lus]

I think I reversed the wires on the coil connections on the OD/clean relay, i'll only have time to check that on sunday, so that'll have to wait.

could that be the weird reason of my issue with the low volume on OD chan ?

[Ang3lus]

You guys think I should use 2 15v 5 watt Zener diodes to drop b+ to 450v ?