DSL40C Tube Combinations:

[Inspector #20]

Been experimenting with different pre-amp tube combos on my DSL40C'S.

One very, very good tube setup that is rely working out well is as follows:

V1: ECC823
V2: ECC83S
V3: ECC83MG
V4: 5751

I'm running this combo in my primary DSL40C, along with standard Electro-Harmonix EL-34's and a custom-mafe WGS Reaper 55Hz speaker.

In my back-up DSL40C, I chose a slightly different approach based on tubes that I had on hand.

I swapped a number of tubes around with lauster results, but then I stumbled o to this combination by accident

V1: 5751
V2: ECC82 (12AU7)
V3: ECC83S
V4: 5751

This combination has a very low noise floor (compared to all 12AX7's) and produces a very smooth overdrive tone, reminiscent of Angus Young.

However, when the Tube Screamer hits the amp, the tone blooms into this thicker, organic overdrive, more skin to a George Lynch rhythm tone, yet very full and articulate.

It's just ok straight outta the amp, but as the pedals are brought online, my goodness does it ever take on a three-dimensional effect.

It's really something to hear each pedal switched on one at a time.

Its amazing!!!

 

[Inspector #20]

The various 12A?7 tubes all have different gain ratings.

Gain Factor
AX=100 mu
AT=60 mu
AY=45 mu
AU=19 mu

But a lot of people look at these numbers and think..."that's all." And it's not.

Unfortunately, there is also this:

Plate Resistance
AX=80K ohms
AT=10.9K ohms
AY=25K ohms
AU=7.7K ohms

While it doesn't hurt these tubes to be swapped in for a 12AX7, it's not ideal either. You want to know why these tubes sound clean? It's because running a 12AU7 or 12AT7 in a circuit designed for a 12AX7 biases them cold, damn near sterile. You aren't actually getting 60 mu out of a 12AT7 in a 12AX7 slot, and you aren't getting anything close to 45 mu from a 12AU7. Preamp tubes are cathode-biased (well, after the '50's anyway) but a big jump in plate resistance will put the tube out of bias range.

Now there is an exception, the 5751 was designed to have a mu of 70, and a plate resistance identical to a AX, the 5751 tube was specifically designed to be a lower-gain, plug-in replacement for the 12AX7. (it is not however considered an ideal replacement for the 12AT7, despite their similar gain factors)

 

[Inspector #20]

Installed and tested a new combination this morning and it impressed with its low noise floor and high volume level:

V1: TAD7025WA
V2: JJ5751
V3: TAD7025WA
V4: JJ5751

With this tube rollout, I'm running 'Lead 1' gain at dial position '4' and the TS-9 gain all the way off and level at 10am.

This gives a very nice "chug" on muted F#'s with complete clarity and it's very loud yet still controllable at stage volumes.

Amp settings taken just now:



Feedback is present, but manageable, which isn't bad consider my volume is almost halfway up and I'm sitting in front of the amp, close enough to lean forward and turn the dials.