12AU7 As Phase Inverter or Cathode Follower in DSL40C???

[bea]

Can you help me better understand that??? I do not recall seeing a 'gain factor' listed for any of these tubes!!!!!

Those are data wise normal ECC83/12AX7 which have a (theoretical) gain of 100. The 5751 is IMHO a low gain variant of the ECC83, AFAIK something around 70. THe tubes on that "family" are not actually a family. Especially the 12AT7 and the 12AU7 are different - they can deliver quite a lot of power. The main thing they have in common is the heater.

 

[ivan H]

THe tubes on that "family" are not actually a family. Especially the 12AT7 and the 12AU7 are different - they can deliver quite a lot of power. The main thing they have in common is the heater.

Yes, these tubes are designed to deliver higher current, especially so the 12AU7. They sacrifice gain to achieve this from the small triodes. This is why we see 12AT7's driving transformer coupled reverb tanks where some gain at higher current is required, & 12AU7's used to drive R/C (resistance/capacitance) coupled reverb tanks where even higher current is required. The 12AU7 supplies enough current to allow them to be used as output devices in very low power (1 watt) amps. Cheers

 

[bea]

The 12AU7 supplies enough current to allow them to be used as output devices in very low power (1 watt) amps.

The 12AT7 as well. Although people are not well aware of that. The 12AU7 has better linearity.

 

[Inspector #20]

Yesterday, I was running my backup amp with a selection of tubes I had on hand.

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

Very good, natural overdrive, no feedback, good dynamics and very low noise, even at 1/2 volume.

 

[Jethro Rocker]

Using one as a PI and reducing the volume can be useful too. My Marshall 4010 has the JCM800 touchy volume control and a lower gain tube makes it easier to adjust in PI.

 

[Inspector #20]

Ok,

If you are shooting for a very classic rock kind of tone, like early AC/DC for example, it's hard to beat a 12AU7 in the V2 position with a standard ECC83 (12AX7) in the V1 spot.

If you want a little less gain and more volume, put a JJ5751 in V1 with a standard 12AX7 in V2.

V3 is the cathode follower position, and the tube used here needs to be tough. Spiral filament 12AX7 tubes have problems in cathode follower circuits due to the fact that most cathode follower circuits in guitar amplifiers exceed the maximum cathode to heater rating of 100 volts. It's also said that you should avoid long-plate tubes in this position in the DSL's because it can cause unwanted feedback.

I tend to stick with a JJECC83s or JJECC83MG here exclusively with good results. However, the TAD7025WA has also worked very well in this position.

Of all the tube combinations I have experimented with, the best tube in V4 continues to be the 5751 or the ECC81 (12AT7)

Now, I am in the habit of using what I have on hand before buying more tunes. That being said, here are some noted substitutions:

The TAD7025WA can be used in any position as you would use a standard 12AX7/ECC83. It is a quiet tube and is rugged.

I often use the JJ ECC803 Long-Plate (because I got quite a few of them) in place of a standard ECC83/12AX7, except in the V3 cathose follower position.

The JJ 12AT7 (ECC81) is a lower gain variant of the 12AX7 and it can be used in place of a 12AX7 - NOTE that I mentioned "JJ 12AT7" specifically - because it is a short-plate tune. The TAD, Electro-Harmonix, Genelex and Mullard 12AT7's are long-plate versions and they don't seem to work that well in the V3 of the DSL's,

Thus far, I am very pleased with the JJ ECC823 in V1, a JJ ECC803 in V2, a JJ ECC83MG in V3 and a JJ 5751 in V4.

Overall, that combination has the most natural, organic gain structure, with rich sustain, absent of fizziness and the cleanest overdriven chug of any combination I have tested....

@Mitch Pearrow SJMP

 

[Mitch Pearrow SJMP]

@Mitch Pearrow SJMP

A very informative post on tube selection, thanks for sharing it and your well found conclusions.
I am going to have to give it a try.
Cheers Mitch

 

[Cadorman]

I have used the 12AY7 quite a bit in V1 or V2 on high gain amps like the 900 series. They work pretty well to tame them down.

 

[Inspector #20]

I have a couple 12AU7's on hand i think....I'm out of most tubes other than a stock of ECC83's

 

[Mitch Pearrow SJMP]

I have a couple 12AU7's on hand i think....I'm out of most tubes other than a stock of ECC83's

I have a number of spares, but none of the low gain type.

 

[Cadorman]

I have a variety of new and old 5751, 12AT7 and 12AY7 tubes if you guys want me to mail some out to Cali to try.

 

[Mitch Pearrow SJMP]

View attachment 35973
I have a variety of new and old 5751, 12AT7 and 12AY7 tubes if you guys want me to mail some out to Cali to try.

That is very generous of you Cadorman

 

[Cadorman]

Send me your address Mitch. I'll send them out this week. I've got my amps all sorted out at this point.

 

[Mitch Pearrow SJMP]

Send me your address Mitch. I'll send them out this week. I've got my amps all sorted out at this point.

Ok but I am broke.

 

[Cadorman]

Ok but I am broke.

Ha! So am I!

 

[Mitch Pearrow SJMP]

It’s been a very lackluster number of months now.
Thanks

 

[Jethro Rocker]

I tame nothing. It's high gain for me! Can always turn gain down. Well, a little anyways!

 

[Inspector #20]

I have a number of spares, but none of the low gain type.

I do....

 

[Inspector #20]

I have a variety of new and old 5751, 12AT7 and 12AY7 tubes if you guys want me to mail some out to Cali to try.

I think I have a couple of new 12AU7's but I am out of 5751's. I am thinking about setting Mitch's amp up with ECC83 in V1, a 12AU7 in V2 and ECC83's in V3 and V4, because I have those in my hand right now. The 12Au7 in v2 will roll off some gain and allow use of 'Lead 2' on the DSL40C....

 

[Inspector #20]