Biasing level for a MARSHALL DSL100H

[zzmoore]

Re: Biasing level for a MARSHALL DSL100H

At some have mentioned, there is not going to be a difference between 33 and 35 mA. Nothing is that stable in an unregulated, tube, guitar amp.
Speaking of unregulated.....neither is the wall supply. I have seen it between 117 and 127 for many years.
The bias range is pretty big. I have "never" heard a 6L6 amp that was not fine at 33mA.

 

[ken361]

Re: Biasing level for a MARSHALL DSL100H

I was told as long there not more 8 ma a part your fine

 

[JeffB]

Re: Biasing level for a MARSHALL DSL100H

Didn't you change to KT-77? Remember the KT-77 is rated at max plate dissipation of 30 watts, instead of 25 watts.

Modern kt 77s bias just like el34s. Ordered same bias point as the previous 3 sets and double checked with tube depot tech (cos I am unedumacated about such things)

 

[JeffB]

Re: Biasing level for a MARSHALL DSL100H

IME, there is a huge differemce when the gap is there between the tubes. The amp becomes fuzzy and harsh ..it sounds like complete ****e.


now for difference between both tubes running at 33 and both at 38 or both at 42, haven't done the testing to say one way or the other. but when there is a sizable gap, I sure as hell can hear it. the tone sucks and I'd rather play my ss practice amp.

 

[cliffenstein]

Re: Biasing level for a MARSHALL DSL100H

I've got a JCM 2000 DSL100 made in 1997 (no bias drift issues...woohoo!). I keep the bias at 74 per side which is way cooler than the recommended 90. I like it a LOT like that and I also like that my tubes will last longer.

 

[ken361]

Re: Biasing level for a MARSHALL DSL100H

8 prb is stretching it lol but I had a mix matched tube same brand 2 EH EL 34 they were like 4ma apart they still sounded fine. But I figured I would get a new set of Tungsols to ease my mind

 

[zzmoore]

Re: Biasing level for a MARSHALL DSL100H

I do not know that i would call 4mA a "miss-match". I would consider 2mA to be a very good matched pair.
The whole bias thing frequently gets overstated.
The first Soldano HR50+ i worked on was enlightening. The OT was Way Lopsided. Something like 127 Ohms on one side and 83 on the other. I thought there was something wrong with the OT.
I called the shop, this was when Bill Sundt was still there, and Bill answered the phone. I talked to him about it. He still had the prototype OT that Merc Mag wound for them, he measured it, and it was almost identical. Mike wanted the amp that way.
"Unbalanced" power tubes are not necessarily a bad thing. Like with lots of stuff.....It Depends.

 

[Lake Placid Blues]

Re: Biasing level for a MARSHALL DSL100H

I do not know that i would call 4mA a "miss-match". I would consider 2mA to be a very good matched pair.
The whole bias thing frequently gets overstated.
The first Soldano HR50+ i worked on was enlightening. The OT was Way Lopsided. Something like 127 Ohms on one side and 83 on the other. I thought there was something wrong with the OT.
I called the shop, this was when Bill Sundt was still there, and Bill answered the phone. I talked to him about it. He still had the prototype OT that Merc Mag wound for them, he measured it, and it was almost identical. Mike wanted the amp that way.
"Unbalanced" power tubes are not necessarily a bad thing. Like with lots of stuff.....It Depends.

In my own experience a slight "mismatch" is often desirable. It seems to add some air and swirl to the tone.

 

[zzmoore]

Re: Biasing level for a MARSHALL DSL100H

In my own experience a slight "mismatch" is often desirable. It seems to add some air and swirl to the tone.

Funny you should say that.
I am not hip to all the In/Latest/Cool descriptives but.......when i was dealing with that Soldano, i talked to them a few times on the phone. I talked to Mike for about 30 seconds.....told him Bill was helping me with that OT.
He said the imbalance suited That Amp, and can add a "Pleasing Swirl" if it is part of the right system.
I had never heard That Term before, so it always, kind of, stuck in my head. :dunno:

 

[ken361]

Re: Biasing level for a MARSHALL DSL100H

I meant that one tube was 8 months old and the newer set that one red plated I used the second tube and used those it sounded fine. I checked the bias twice after the older tube was alway 4 ma behind but still sounded fine

 

[misterwhizzy]

Re: Biasing level for a MARSHALL DSL100H

I'm just glad the posters in this thread finally got around to talking about current in terms of milliamps instead of millivolts.

 

[LLL]

Re: Biasing level for a MARSHALL DSL100H

(Bias according to the power tube, not the amp)

 

[LLL]

Re: Biasing level for a MARSHALL DSL100H

Here's how ya bias (I will not be held responsible for any stupidity).

The cathode resistor method is recommended if you don't have handy-dandy biasing jacks built-in to the amp:

http://www.duncanamps.com/technical/lvbias.html

Also take note of the MAX values for each type of power tube (further down the document) and adjust accordingly.