SE amp using 1619 instead of 45 triode

[rcavictim]

Has anyone out there made a single ended class A amp like you'd find done for the magic sound of a directly heated tube with a 45 triode but using the 1619 instead, maybe because like me they have some 1619's but no 45's?

The 1619 has a 2.5 volt, 2 amp directly heated cathode and is a metal octal beam power pentode with outward appearance and ratings similar to the metal 6L6. According to the RCA datasheet in A1 with 300 volts anode, 250 volts G2, it can make 3 watts RMS into an 8K load at 7% THD with 10 volts drive. This is almost 2A3 territory! This makes me wonder if it may have some potential wired in triode mode with more drive signal. This tube can also be run into A2 territory or AB2 in P-P where a pair will make a respectable 36 watts at just 2.5% THD.

I'd like to have a low power SET amp with amazing tone like a 45 to use to test high efficiency speakers, but I don't want to pay the price for 45's. I have a dozen NIB 1619's here to play with. I could even run two in SE parallel. The datasheet does not address triode connection for this tube.

Any experience based comments or ideas welcomed.

[Fuling]

As 1619 is similar to 6L6 two things pop up in my head:
Cathode feedback and/or RH807.

[Bandersnatch]

1619 is more like a 6V6.

It does quite well with 10k a-a, and a 300V/40 mA OP. G2 to 20% or so. Try getting a Peerless 16309 wound with taps at this point. The Dyna Z565 has worked well for me, until I had a specially prepared S265Q wound. The little valve did not seem to mind the extra Iron...:-)

The major downside is the low grid circuit resistance, this valve loves a grid choke.
cheers,
Douglas

[rcavictim]

Originally posted by Bandersnatch
1619 is more like a 6V6.

It does quite well with 10k a-a, and a 300V/40 mA OP. G2 to 20% or so. Try getting a Peerless 16309 wound with taps at this point. The Dyna Z565 has worked well for me, until I had a specially prepared S265Q wound. The little valve did not seem to mind the extra Iron...:-)

The major downside is the low grid circuit resistance, this valve loves a grid choke.
cheers,
Douglas

Douglas,

Thanx for the input.

Thing is, I actually have quite a large tube inventory and have many that are suited for P-P operation. I have some very good sounding P-P amps already and am not interested in another P-P. I am after the magic that I and others have heard in the oddly distorted (inserted to pacify the critics ) output of a SET amp. In addition to SE there seems to be something magic about DH cathodes which allegedly contribute to the tonal character of this class of amp which is lost when sleeved cathodes are used. This property rather limits the selection of suitable tubes for SET Hi-Fi service to purists of this mindset (little pun in there).

My favorite amp is my 300B driven, direct coupled 805 SETriode amp. With 40 W RMS available per channel on near 100 dB efficient speakers the low frequency distortion often heard from 300B SET amps is a non issue and diistortion is vanishingly small. This SET amp noticebly betters my best P-P amps for tone and 'presence'.

Thanx for the tip on using a grid choke with this tube. I will have to try this. My inventory of SE output xfmers is almost nil so I will heve to be creative as usual.

I guess I should consider a DHT for the input line amp/driver stage. Perhaps one of those battery radio triodes? This project could be interesting if it ever gets to the breadboard stage!

[rcavictim]

Originally posted by Fuling
As 1619 is similar to 6L6 two things pop up in my head:
Cathode feedback and/or RH807.

What do you mean by RH807?

[rdf]

What do you mean by RH807?

That's member Alex Kitic's circuit:

http://www.tubeaudio.8m.com/807/807.html

[Bandersnatch]

Originally posted by rcavictim


Thing is, I actually have quite a large tube inventory and have many that are suited for P-P operation.

Well now, you have me curious about your thought process. What quality makes a tube good for PP?

If there is a g2, I would take advantage of it. See Pet Millet's SE version of the E-Linear circuit in an early '05 AudioXpress. He used KT88's but I have a feeling that the 1619 wold make an excellent lower power version.

It is almost enough to contact Jack of EP for an E-linear tapped, 5k/50 mA SE OPTx. 20 and 30% I think would be best. I'd probably do it with an HY69 though...can't get away from the glass envelope and thoriated tungsten....
cheers,
Douglas

[rcavictim]

Originally posted by Bandersnatch


Well now, you have me curious about your thought process. What quality makes a tube good for PP?

Filament continuity is a good indicator. Actually many power tubes could likely make fair P-P amps including many TV horizontical sweep tubes. With the supression of even order HD in a P-P design tubes can be less linear and even tubes that would be atrocious in pure class A can be used because class AB and even B operation is a possibility when considering P-P (fidelity being compromised of course).

[i]
If there is a g2, I would take advantage of it. See Pet Millet's SE version of the E-Linear circuit in an early '05 AudioXpress. He used KT88's but I have a feeling that the 1619 wold make an excellent lower power version. [/B]

Yes, the 1619 has a G2. I am not really interested in any UL scheme in my SET amp idea. Pure triode sound is my goal. Mind you, if I were to relax my specification in this regard UL would be the good choice I'm sure.

[i]
It is almost enough to contact Jack of EP for an E-linear tapped, 5k/50 mA SE OPTx. 20 and 30% I think would be best. I'd probably do it with an HY69 though...can't get away from the glass envelope and thoriated tungsten....
cheers,
Douglas [/B]

I really have no plans to spend any serious coin on components. This will be a 'junk box' sourced amp if it happens. That eliminates any possibility to purchase fancy output iron. This could end up using P-P output iron in a cap coupled arrangement with a choke plate load. If I was prepared to buy iron, I'd also likely be prepared to purchase 45 tubes as well. I agree that it would be nicer to actually see the DH filament working inside a glass bottle. Unfortunately the 1619 is a metal shell tube.

Another idea if I wanted to play with more power (but that is not what I need) would be to use the 1619 as a driver for perhaps an 811A in SET. My primary need for this amp is as test equipment to qualify high sensitivity speaker systems for audio fanatics insisting on trying to hear dynamic music from flea power SET amps. Right now I use a SE 6BQ5 stereo amp pulled from a Magnavox console but this is not sufficient to actually qualify a speaker IMO so no sales have been/will be made with inadequately supported claims.

[Bandersnatch]

The even order HD cancellation only happens when both tubes are conducting. It only works well, when both tubes are swinging equal amounts in oposite directions. That only happens in Class A.

Why anybody would go to the trouble of DIY-ing an amp, and not planning on a Class A bias operation is hard understand. If I want more power, one just picks a proper valve, instead of going into AB...power is just a side effect of PP, it isn't the goal.
cheers,
Douglas

[rcavictim]

Originally posted by Bandersnatch
The even order HD cancellation only happens when both tubes are conducting. It only works well, when both tubes are swinging equal amounts in oposite directions. That only happens in Class A.

<snip>
cheers,
Douglas

Thanx for pointing this out. I never really gave that much thought and I certainly do not claim to be a tube amp expert, although it is one of my many hats worn well enough to be comfortable.