6CJ6 and 6DL5 PP revisited

[murrayatuptown]

6CJ6 and 6DL5 are both suitable for PP amps with about 10k P-P load.

There is a Philips amp or 2 discussed here previously for Kaliostro, I believe.

The 6CJ6/EL81 datasheet I think only presents Class B data. I don't have any objection to Class B or 10k output transformer. (Or anode clips).

6DL5 datasheet has PP data for both Class AB1 and B, with not much power output difference. Main difference obvious is bias and maybe drive or OD characteristics.

This makes revisiting 6CJ6 PP AB1 questions/discussion less of a dead end.

Class B guitar amps aren't terribly common...I vaguely recall perhaps a Music Man or Peavey example cited.

I had always simply avoided Class B for audio, but if it worked for Philips (more traditional non-OD usage), a useable circuit exists.

Any insight on why Class B might be something to avoid for a guitar amp?

Thank you

[PRR]

Build to class B suggestion (which is really a cool AB), then re-bias to about 70% of Pdiss, it will be warm AB.

But why this tube?? It takes much more heater power than EL84. It has much less Pdiss (limiting how hot you can idle it). Grid drive voltage is very high, like 3X the drive of an EL84-team. And you can't buy a EL81 on a Saturday night.

> 6CJ6 and 6DL5 are both suitable for PP amps with about 10k P-P load.

The sheets I find clearly say 2.5k. If you use 10K you get like 1/4 the power, Champ territory. (Which is pathetic for 2.1 Amps of heater current.) 10k would "be right" if B+ were raised to 400V, but the tube is rated for 300V, and reasonable circuit balance leads to Vg2 down near 100V, awkward in light of the large swing in G2 current.

[silverfox]

Build to class B suggestion (which is really a cool AB), then re-bias to about 70% of Pdiss, it will be warm AB.

But why this tube?? It takes much more heater power than EL84

Regarding History: So what would have been the original application for these tubes. Sounds like designs of the time were inefficient or was it the components that limited the applications?


silverfox.

[Tony Bones]

According to the datasheets, the 6CJ6 and 6DL5 are very different tubes. The external plate terminal on the 6CJ6 suggests that it was intended for high frequency operation. Maybe a small radio transmitter? Perhaps driving the grid of a larger transmitting tube? (I'm just guessing.) OTOH, the 6LD5 has very low heater current (0.2A) and the datasheet recommends it for car radios.

Although not explicitly stated, it looks like the 6DL5 biases at a much lower grid voltage so would much easier to drive.

Having said that, 1.05A of heater current wouldn't bother me unless I was trying to use an existing PT with limited heater power available.

{edit: removed quote-marks which munged URLs -PRR}

[DummyLoad]

perhaps the 6AR5 is another candidate? still plentiful and relatively inexpensive NOS. for low power, 6V6 with 200-250V is where where i'd lean to. 


https://frank.pocnet.net/sheets/127/6/6AR5.pdf

--pete

[murrayatuptown]

Not in order of importance:

TB: original application for 6CJ6/EL81 I think was a TV or CRT sweep circuit.

PRR (IIRC):
Why this tube...because I have a box full. Heater current is inoffensive because I have a lot of power transformers with high current 6.3V windings and separate filament-only xfmrs w/8-20 A ratings.
This tube (PP) looks friendlier than 6AS7/6080 PP (yeah, another box lurking in the basement).

3rd person (sorry, can't see on phone since I started typing) noting 6DL5 & 6CJ6's are very different.:

Yes, I tend to leap from one thought to another with little warning...I picked up apparently wrong info somewhere that they both had similar plate load preferences.

Trying to use what I have before hoarding other sweep tubes from ESRC dollar menu I don't really need or have room for.

2.5 k p-p isn't as inconvenient as 10k, though.

Thanks

Murray

[PRR]

> The external plate terminal on the 6CJ6 suggests that it was intended for high frequency operation.

Says on the box (sheet): "Line time base". What we in the US call "TV Horizontal Output". Put a big deflection choke in the plate circuit. Drive the tube ON then OFF. Goes to high I low V, then to low I high V. The plate kick-up will be thousands of volts. Hence we can't put the plate pin with the others, but a good distance away.

No idea way it has suggested use as an audio amplifier. Yes, it will; but other common tubes will do the job better.

It "could be" a Class C RF power amp for the lower frequencies. H-sweep tubes were common in non-commercial MF transmitters. (HF work wants a more compact tube and specialized seals.) Again, there are other choices.

[murrayatuptown]

Yes, the 2.5k a-a is plain as print on datasheets.

Duh (for me...PRR & others might have been thinking that).

I think the supporting history of using EL81's as PP and PPP are two Philips (PA?) amps of two different power levels (20 & 40 W?).

If you have tubes & usable transformers it's...just...hard...to say goodbye to the tubes...maybe I have an evil twin somewhere shopping eBay  that wants to end up in the same situation.