The new dumble modded bassman build video series... begins!

[pompeiisneaks]

Nope going to use the same setup as the dumble modded bassman which uses 6L6GC's. For 4 at 900mA and 4 12AX7's with 300ma each, the math adds up to 4.8mA current though...

SO that may mean I want the iron for the dual showman/dual reverb: P-T290FX

Those stats are:
P-T290FX 368VA 120VAC Primary 60Hz 640Vct Secondary@518 mA 60V Bias Heaters - 6.5V @ 5.5A

BUT that seems to have a lot higher B+ and i'm not sure we had measurements of what it's supposed to be?

Or should I stick to the first PT and cut back to a 50 watter?

~Phil

[professormudd]

So as far as the chassis goes, are you having one custom made or are you going to fabricate it?

[donvan]

Nope going to use the same setup as the dumble modded bassman which uses 6L6GC's. For 4 at 900mA and 4 12AX7's with 300ma each, the math adds up to 4.8mA current though...

You have a typo - "4.8mA". Should be amps, not milliamps.

[pompeiisneaks]

So as far as the chassis goes, are you having one custom made or are you going to fabricate it?

Going to get a custom one made for me from this ebay seller:

https://www.ebay.com/itm/Custom-Amp-Cha ... 3674193825

I've gotten one from him before and it was excellent quality work.

~Phil

[pompeiisneaks]

Nope going to use the same setup as the dumble modded bassman which uses 6L6GC's. For 4 at 900mA and 4 12AX7's with 300ma each, the math adds up to 4.8mA current though...

You have a typo - "4.8mA". Should be amps, not milliamps.

Oh yes, thanks...

Still would like someone to confirm the last suggested transformers work. Not sure if the dual showman/dual reverb transformers are too high B+ or just fine?

~Phil

[didit]

... stick to the first PT and cut back to a 50 watter?

It's supposed to be a modded Bassman so the answer is obvious, no?

Best .. Ian

[pompeiisneaks]

... stick to the first PT and cut back to a 50 watter?

It's supposed to be a modded Bassman so the answer is obvious, no?

Best .. Ian

If it was obvious I wouldn't be asking the question... a bassman can be either 50 or 100 watts. I was going to make it 100, but the bassman PT's I'm seeing don't seem to have the amperage to handle the 4 power tubes.

Are you saying' it's obvious I can't do a 100W or it's obvious I have to up rate the PT for the 100 W or? Or is it obvious that there's a different Bassman PT I'm not suggesting? The bassman 135? What part is obvious that I'm missing?

Clueless in Seattle.

Edit: fixed a wrong thing.

~Phil

[didit]

... stick to the first PT and cut back to a 50 watter?

It's supposed to be a modded Bassman so the answer is obvious, no?

Best .. Ian

If it was obvious I wouldn't be asking the question... a bassman can be either 50 or 100 watts. I was going to make it 100, but the bassman PT's I'm seeing don't seem to have the amperage to handle the 4 power tubes.

While there are/were amps called Bassman100 from Fender out there, the one modded and reverse engineered was classic lineage 50W, which was the point (if there was one).

Best .. Ian

[pompeiisneaks]

Oh that absolutely makes sense, and I do think now that you mentioned that, it does make more sense for me to make it 50W.

I'll just adapt back towards the original more closely, and then use the first referenced 'bassman pt' as the 4A will be fine to cover the now required (4.8A - 1.8 for two 6L6GC's) 3.0A ... so we've got plenty of breathing room. (or put another way 2X6L6GC = 1.8A + 4X300mA = 1.2A or 3.0A)

Mathing...

Thanks,

~Phil

[BarryW]

most 100w D style amps would use Twin Reverb iron. That would be my choice for 4 - 6L6, the 290FX typically

[pompeiisneaks]

Ok new question. Was about to put all the parts into the cart and the choke fender would use, 022699, has 4H and 90mA, and 108 ohm as it's rating, but nowhere can I see any equivalent.

I know that if I go up in mA rating, it's likely to change the resistance, I think it would go down due to thicker wire being able to handle more current also ends up with less resistance no? I see one for 4H and 225mA which does have a bit less resistance (65 ohms) but I think it's so minimal as to be a non issue. half the resistance yes, but the voltage drop over those two are both going to be pretty insignificant?

Or do I want to go more for higher henry rating, but get closer to the 108 ohm resistance? For example there's a 5H 150mA and 108 ohms?

Don't really know enough about the inductor to know what's best. I know the higher the henry rating, the more filtering it does, so you'd get cleaner power, but don't know how much 1H matters?

~Phil

[pompeiisneaks]

Oh another silly question. I seem to have forgotten to order the 25uF cathode bypass caps, but I did recently do a build that ended up not being used, that has some 10uF Wima 63VDC caps I could re-use. Thoughts on how much frequency loss I get from that?

From a typical rc calculator, with 10uF and 1.5k I get a freq of 10.61 hz. but at 25uF I go down to 4.24 hz

Both seem well below a BASS guitar which seems to normally go down to maybe 41 Hz? So I'd think if I use those 10uF's I'm probably fine right?

~Phil

[Smokebreak]

Yes, 25uf or 10uf, or 3.3uf, or 1uf or .68 makes a massive difference once you add up everything else. You would have to change the recipe a bit if you want to use 10uf. It simply will not sound the same as 25uf, with everything else the same.

[pompeiisneaks]

Yes, 25uf or 10uf, or 3.3uf, or 1uf or .68 makes a massive difference once you add up everything else. You would have to change the recipe a bit if you want to use 10uf. It simply will not sound the same as 25uf, with everything else the same.

Maybe I didn't ask the question correctly.

Will 10uF be a significant difference for tone for a guitar? It seems insignificant for bass, but may have some impact there, but I"m building a guitar amp.

~Phil

[norburybrook]

Yes, 25uf or 10uf, or 3.3uf, or 1uf or .68 makes a massive difference once you add up everything else. You would have to change the recipe a bit if you want to use 10uf. It simply will not sound the same as 25uf, with everything else the same.

Maybe I didn't ask the question correctly.

Will 10uF be a significant difference for tone for a guitar? It seems insignificant for bass, but may have some impact there, but I"m building a guitar amp.

~Phil

Phil , are those calculations correct? They seem too low frequency wise. At those frequencies there'd be no audible effect on a guitar signal.

From my experience one of the good things dumble did was reducing the bass by reducing the cathode caps from a 25uf to 5uf , this stops the amp falling apart at volume. I would say a 10uf would be a good thing for an amp that's going to be pushed into overdrive especially if using humbuckers.


M