6V6-6L6 in amp

[Telenut62]

I've noticed some amp builders have an option of either 6V6 or 6L6 tubes in their amps. I was wondering is it a straight swap or do you need a beefier OT?
And what would the result be with the 6L6's....higher power output no doubts and more headroom?

[tubeswell]

I have built amps that can take both types.

The PT needs to be spec'd to handle 6L6s as they draw 2 x as much current as 6V6s. (Look at the tube data-sheets)

The OT should ideally have multiple taps on the secondary winding to enable you to shift the load resistance easily. A 6V6 requires about 2 x as much load resistance as a 6L6.

You also need to be able to adjust the bias voltage. (The current draw needs to be such that the idle dissipation is 60-80% of maximum for Push pull, class AB1 operation. For a 6L6, this will mean more plate current than what a 6V6 needs)

[jefrs]

Putting a 6V6 into a 6L6 amp -
If the amp is cathode biased and has the HT no higher than suitable for 5881 = 6L6WGB then the JJ-6V6S = JJ-6V6GTS may be fitted. The JJ is perhaps the only 6V6 type that can take the extra HT voltage, and it seems to be bullet-proof. It does not appear to be a true 6V6 but a low-current heater 5881 type, it does however sound like a good 6V6.

You will not notice a reduction in volume by swapping to a JJ-6V6S compared to a 6L6GC but it will sound different, and you will be over-loading the JJ-6V6S, but they don't seem to mind. They seem to take a ridiculous plate current for a 6V6.

Similarly putting 6L6GC into a 6V6 amp will not give you much greater power, the gain/output is primarily designed into the circuit. Most multiple output bottle type amps are cathode/self biased because you can then just swap the bottles out.

Most OT are a compromise somewhere between the requirements for 6V6, 6L6 and EL34. Guitar amps are usually mismatched, and don't care. Do check. This is something that can get at least partially sorted with the bias.

With a cathode bias, you do not adjust the grid bias because the thing is self-biasing. The cathode resistor is near-enough for all common octal types, as is the output transformer load (because it is self-biasing). Typical bottles -
JJ-6V6S, 5881/6L6WGB, 6L6GC, EL34, KT66, KT88, etc (watch out for pin1 on true pentodes).

[hackworth1]

Gerald Weber says that if the heater voltage tests at 6.1 volts or better with a 6L6 installed, you are good to go. If it falls to 6v flat, you're no good. He also generally recommends the 5AR4 rectifier over the 5y3. Be mindful of appropriate bias in fixed bias designs when tube swapping.

[kleuck]

Originally Posted by jefrs

it does however sound like a good 6V6.

I strongly disagree, they sound like 6L6.
Sold mine for this very reason.

Originally Posted by jefrs

With a cathode bias, you do not adjust the grid bias because the thing is self-biasing. The cathode resistor is near-enough for all common octal types, as is the output transformer load (because it is self-biasing). Typical bottles -
JJ-6V6S, 5881/6L6WGB, 6L6GC, EL34, KT66, KT88, etc (watch out for pin1 on true pentodes).

Definitively NO , a cathode resistor meant for 6L6 will just mean an idle current able to cook a 6V6 in a few weeks (except i suppose the JJ, as it's plate is an 6L6 one), even though they are sturdy.
Neither is the load, 6L6 OT gives about half the ratio needed for 6V6.

[celeste]

Originally Posted by kleuck

I strongly disagree, they sound like 6L6.
Sold mine for this very reason.

I have to agree with you on this one

Definitively NO , a cathode resistor meant for 6L6 will just mean an idle current able to cook a 6V6 in a few weeks (except i suppose the JJ, as it's plate is an 6L6 one), even though they are sturdy.
Neither is the load, 6L6 OT gives about half the ratio needed for 6V6.

I have to disagree with you on this. The 6V6S is a redesign of an Eastern tube that had no western equivalent. The plate structure dates back to well into the Telsa days. Despite the spec sheet calling it a 14w tube, it is very safe at 18w.

If the B+ is low enough for a 6V6, then you can swap them and 6L6's without danger in a cathode biased amp

If the OT has the secondary taps, the impedance is not an issue, if an 8 ohm load on the 8 ohm tap reflects a 4200 ohm load, then that same 8 ohm load on the 16 ohm tap will reflect an 8400 ohm load. When you change tubes, you also change taps.

[kleuck]

That's why i said the JJ can probably stand the power, but even with a low voltage, you cannot sub a regular 6V6.
I put a twin bias in my SP6 to use both 6V6 and 6L6, voltage is low for a 6V6 (350 volts) and believe me, when i made a mistake and put a 6V6 with the 6L6 cathode resistor, it was frying (i burnt my finger after only a couple minutes, and within 1/4 second, i mean really burnt)

Of course with taps the ratio is not an issue...that's exactly how i proceed with the SP6.

[celeste]

Originally Posted by kleuck

...(i burnt my finger after only a couple minutes, and within 1/4 second, i mean really burnt)
...

Ouch, I hate it when I do things like that, and they don't let you forget.

[Telenut62]

Ok I think I'm getting the picture...if you are running 6V6's as the norm, then to put in 6L6's the B+ is in by spades but the current is higher. I thought with the OT secondary taps, if you were on 8ohms with the 6V6 then with the 6L6 it needs to be 4ohms?.....aaaaargh now I'm confused.

[Telenut62]

Ok I think I'm getting the picture...if you are running 6V6's as the norm, then to put in 6L6's the B+ is in by spades but the current is higher. I thought with the OT secondary taps, if you were on 8ohms with the 6V6 then with the 6L6 it needs to be 4ohms?.....aaaaargh now I'm confused.

[kleuck]

If your amp is an 6V6 SE one, don't worry, you can put 6L6 if we are talking B+, bias etc, the idle current will be lower.
But for the best load, you need to connect your 8 Ohms speaker in the 16 ohms output (6L6 in place of a 6V6)
For the best bias, you need to change the cathode resistor.
6V6 in a 6L6 amp : no.

[jefrs]

Originally Posted by kleuck

If your amp is an 6V6 SE one, don't worry, you can put 6L6 if we are talking B+, bias etc, the idle current will be lower.
But for the best load, you need to connect your 8 Ohms speaker in the 16 ohms output (6L6 in place of a 6V6)
For the best bias, you need to change the cathode resistor.
6V6 in a 6L6 amp : no.

I did say the JJ-6V6S was the only 6V6 you can put into a 5881 amp - because they can stand the abuse.

However they do not sound like 6L6, at least not Sovtek 6L6WXT+, GE-JAN-6L6WBG or =C=6L6GC
They do look like a 5881, something like the GE-JAN-6L6WGB but with shorter plates, not the big bottles of the Sovtek or Svetlana. Their crisp clarity places them firmly in the 6V6 camp, not the big open sound of the 6L6 types. Perhaps they don't suit pukka olde school 6V6 amps, I have only used them in a Bassman clone running HT at 418VDC.

You do have to dig around for the valve data because the Rk is not normally stated.
A single 6V6 wants around 250ohm, 6L6 wants around 200ohm but depends on HT and grid2. Cathode bias is never exact because we are stuck with preferred values, and near-enough is generally good-enough. There is an overlap area.
Again, optimum load for a single 6V6 is 5000ohm to 8000ohm, but a 6L6 wants 3000ohm to 4500ohm but commonly gets a 5000ohm plus OT (turns ratio to speaker load) which will suit both.
It is not ideal but self-bias is just that, it self limits, and within reason is do-able.
The fact of the matter is that you /can/ swap octal bottles about with some degree of impunity, on cathode bias.

[kleuck]

Depends mainly on the chosen impedance and voltage, in most actual amps 6V6 needs more like 500 ohms cathode resistor, 6L6GC about 220-250.

[Telenut62]

Originally Posted by jefrs

I did say the JJ-6V6S was the only 6V6 you can put into a 5881 amp - because they can stand the abuse.

However they do not sound like 6L6, at least not Sovtek 6L6WXT+, GE-JAN-6L6WBG or =C=6L6GC
They do look like a 5881, something like the GE-JAN-6L6WGB but with shorter plates, not the big bottles of the Sovtek or Svetlana. Their crisp clarity places them firmly in the 6V6 camp, not the big open sound of the 6L6 types. Perhaps they don't suit pukka olde school 6V6 amps, I have only used them in a Bassman clone running HT at 418VDC.

You do have to dig around for the valve data because the Rk is not normally stated.
A single 6V6 wants around 250ohm, 6L6 wants around 200ohm but depends on HT and grid2. Cathode bias is never exact because we are stuck with preferred values, and near-enough is generally good-enough. There is an overlap area.
Again, optimum load for a single 6V6 is 5000ohm to 8000ohm, but a 6L6 wants 3000ohm to 4500ohm but commonly gets a 5000ohm plus OT (turns ratio to speaker load) which will suit both.
It is not ideal but self-bias is just that, it self limits, and within reason is do-able.
The fact of the matter is that you /can/ swap octal bottles about with some degree of impunity, on cathode bias.

Yeah thanks for that, slowly getting some idea how it all ties in and working out scenarios where this might be a handy thing to have.

[kleuck]

Here is a chart of what i get (got, slightly hotter bias now, i need to make a new one)



B+1 = anode voltage
Irk = cathode current (total, so plate+ screen)
PA=anode power
Irk = cathode resistor

[tubeswell]

Those 6P3S are good value for money but IME they don't like higher voltages. I'd stick to around 350 max. On the other hand the 6P3Se runs comfortably at around 450. JM2CW

[kleuck]

I did not replace the PT -and don't plan to-, that's the actual voltages with the stock Special PT
One thing i love with the 6P3S, is the "6V6-like" sound, not exactly the same of course, a little more "glassy" and you get less crunch, but imo, at least in SE amps, way better than any 6l6/5881, apart from the crunch, they are more "lively" with just the perfect (at least "good") touch of compression.
Tested in the VHT SP6, see the VHT SP6 mods topic for more info (schematics etc).

6P3S-E seem to be very hard to kill, but beware, you can do a lot of crazy things with AB1 push-Pulls, not with SE or PSE.

[jefrs]

Originally Posted by kleuck

Depends mainly on the chosen impedance and voltage, in most actual amps 6V6 needs more like 500 ohms cathode resistor, 6L6GC about 220-250.

I was quoting from data sheets for a single valve in Class A

6V6 wants Rk 232ohm at 250V and -12.5V on g1 for 5000ohm load
and Rk 317ohm at 315V and -13V on g1 for 8500ohm load
Typical p-p Rk is 225ohm for both [Radiotron]

6L6-GB wants Rk 167ohm at 250V and 14V (-ve?) on g1 for 2500ohm load
and Rk 218ohm at 300V and 12.7V on g1 for 4500ohm load [RCA]

Fyi my Epi BC30 uses a 250ohm Rk for both 6L6WXT+ running at 418VDC, values for p-p not being the same as SE.

[kleuck]

Originally Posted by jefrs

I was quoting from data sheets for a single valve in Class A

6V6 wants Rk 232ohm at 250V and -12.5V on g1 for 5000ohm load
and Rk 317ohm at 315V and -13V on g1 for 8500ohm load
Typical p-p Rk is 225ohm for both [Radiotron]

6L6-GB wants Rk 167ohm at 250V and 14V (-ve?) on g1 for 2500ohm load
and Rk 218ohm at 300V and 12.7V on g1 for 4500ohm load [RCA]

Fyi my Epi BC30 uses a 250ohm Rk for both 6L6WXT+ running at 418VDC, values for p-p not being the same as SE.

Do you know an actual guitar amp running 6V6 or 6L6 at such low voltages ?
Do you know an actual modern amp built to run 6L6GB ?
These datas are just examples, that are useless under another voltage or with another load, you have to draw lines and make calculation, and always end up with very different values for different tubes.
Just look at my chart.
Your amp is a Push-Pull, not a SE, and actually your cathode resistor is a 500 ohms one for each tube.

[No457 Snowy]

A perfect example of this type of amp is the Trinity Tramp, which is also available as a kit. I'm in the process of getting my Tramp kit configured with Stephen right now, I'm ordering/building it as a Head kit and he is currently custom tolexing the Head cabinet for me.

The amp is approximately 6W when run with a 6V6 tube or 12W when run with a 6L6 tube, a fantastic and versatile little amp.

Trinity Tramp


Snowy