3A/110B into a LL1680 Preamp

[stigla]

Hello all!

I recently scored a neat supply of some nice STC 3A / 110B DHT triodes!
http://frank.pocnet.net/short/054/0/094.pdf

This triode have a nice rp of ~5,5k and a mu of 12 and a 4V / 0,25A heater!
A perfect candidate for a Transformer coupled, battery heated preamp

So looking about in the Lundahl catalog I noticed the LL1680.
http://www.lundahl.se/pdfs/datash/1680.pdf

A prim.ind. of 210 at 5mA and a 15K/600 (or 150) ohm impedance ratio. Seems perfect for this triode! So I am strongly considering ordering a pair gapped for 8mA. But I thought I'd check with you guys first.

What will the inductance be for a 8mA gapped type? My calculations says I need at least 150H (~10Hz).

If a 8mA type gives to low inductance I will considder making a ParaFeed preamp with a Gary Pimm BBMCCCS. Should I order a "un-gapped" LL1680 then?

Any other suggestions also apprechiated

Stigla

 

[fdegrove]

OPT.

Hi,

If a 8mA type gives to low inductance I will considder making a ParaFeed preamp with a Gary Pimm BBMCCCS. Should I order a "un-gapped" LL1680 then?

I feel you could just as well order the gapped model so you can experiment with what suits you best.

Cheers,

 

[stigla]

Hmmm, yeah, think I'll do that! thanx!

stigla

 

[siu sin man tho]

hi,

if U use the un air-grab pre-amp output must use cap couple.
If not like to use the cap couple. choose a preamp output trans that can pass current. 10~15ma is safe.
too low will easy to cause saturation of core will weak the bass.

thansk

Thomas

 

[EC8010]

Is silicon heresy?

If it isn't, you could make a constant current anode load out of a semiconductor cascode using BC558B at the top, and MJE340 at the botton. Then, use the transformer in a parafeed circuit of your choice, and don't worry about gaps. The cascode would also greatly improve the stage's rejection of power supply hum.

Of course, I may have broken a taboo by suggesting semiconductors and directly heated triodes in the same breath. On the other hand, it would certainly be different.

 

[siu sin man tho]

To EC8010,

do u know the air gap is physically better than the parafeel design. I agree that parafeel can slove this proble, But still use air gap is better.

thanks

Thomas

 

[Brett]

Re: Is silicon heresy?

Of course, I may have broken a taboo by suggesting semiconductors and directly heated triodes in the same breath. On the other hand, it would certainly be different.

The tube flat earthers may object, but it's nice to have some company.

 

[analog_sa]

I've always tried to grasp the sonic philosophy of parafeed. Other than allowing the use of puny transformers and still have bass i can't see any advantages. You have to accept the slight rounding of transients every transformer imposes plus the added flavour of a coupling cap. The whole idea of transformer coupling for me is to remove an electronic hash even the best caps impose, so why reintroduce it?
Ditto for the silicon. Maybe a FET CCS can coexist with valves but two bipolars?


cheers

peter

 

[stigla]

Hi guys!

Nice to have an old tread back again!

Here's what I did:

I ordered the 8mA gapped types. I have them, and the tubes, and everything! I will use the Easter holiday to put them together.

As implied by fdegrove I thought it would be the wisest thing to do. I will try this normal setting first. Why use a Cap AND a transformer right?

Lundahl stated that 8mA gap will leave me with a Prim. Ind. of ~130H, so I'm a little worried that bass will be a bit weak, but we'll see (one formula I found at Steve Banch's site gave me a -3dB point at ~7 Hz and that would'v been nice if this is right)

If this is not the case, I'll try a Gary Pimm BBMCCS and not use the low impedance output in a Parafeed configuration.

Another thing that cought my attention lately is the fact that the Miller capacitance of the 3B/110B is 133pF!! Thats quite high, and now I'm worried about the HF rolloff as well, since I plan to use a 50k pot. (my CD player needs at least 50k...)

Thanks for your interest guys, I really appreciate it!

stigla

 

[slowmotion]

Re: Re: Is silicon heresy?

The tube flat earthers may object, but it's nice to have some company.

Don't you know that transistors are the work of the ???

 

[slowmotion]

stigla,

This sounds like a great project.

If you try out Gary Pimm BBMCCS ,
it would be interesting to hear how you like
them after having tried normal transformer coupling.

Don't worry to much about the Miller capacitance,
build it first, and see how it works, you can allways change it later.

Good luck!

 

[stigla]

Slowmotion;

Thanks for your uplifitng words! I think I will try the BBMCCCS loading as well since I have all the parts for that too. I will report back when I have made some listening tests.

Hilsen

Stig

 

[siu sin man tho]

hi,

I try LL1680 compare with NP-126 vintage UTC LS50 in same circuit.
Je lab pre-amp.
pls click,

http://users.starpower.net/je2a3/JELsc-TClinepre.jpg

I use 26,76.56 6j5 to test.
U will see the circuit is very simple, then the different of trans will easy to reflex to the result.

the result is np-216 is the best, ll1680 second & ls50 is worse than this two.

The most reason for the pre-amp output is the core must large than pass 15~20ma current. LL1680 only 5ma.
If use different tube had a large current. The core will easy to saturate. Then the high freq & bass will less.
certainly U can use one cap couple between the trans & tube. But If the trans was a quality one & enough current. Why not direct couple?????

Hope U will agree.

thanks

Thomas

 

[Brett]

hi,

I try LL1680 compare with NP-126 vintage UTC LS50 in same circuit.
Je lab pre-amp.
pls click,

http://users.starpower.net/je2a3/JELsc-TClinepre.jpg

I use 26,76.56 6j5 to test.
U will see the circuit is very simple, then the different of trans will easy to reflex to the result.

the result is np-216 is the best, ll1680 second & ls50 is worse than this two.

The most reason for the pre-amp output is the core must large than pass 15~20ma current. LL1680 only 5ma.
If use different tube had a large current. The core will easy to saturate. Then the high freq & bass will less.
certainly U can use one cap couple between the trans & tube. But If the trans was a quality one & enough current. Why not direct couple?????

Hope U will agree.

thanks

Thomas

Hi Thomas,

If you're going to do a comparison like this, at least make sure all the parts used are appropriate for the circuit. You said <i> the core must large than pass 15~20ma current. LL1680 only 5ma.</i> which means it's not a useful transformer for this application, an LL1660/18mA would have been better and then the test would have been fair. I don't have the UTC LS50 to compare specs to see where it would saturate. At best you could have tried them in parafeed, providing you kept the ratio of choke to trans inductances fairly constant or used a CCS for an anode load.

 

[siu sin man tho]

brette.

I test in je lab pre amp circuit is in the same condition.
Now I hadn't LL1660/18mA on my hand, I will order one to test, later I will post the result.

thanks for your opinion.

Do U test or try the NP126 experience?
I had trial,WE, NE UTC LS50& LS151 on hand, so I can test them
in same circuit.

I still find the permalloy core pre-amp output. I know new build james had but too expensive.

thanks for your opinion.

Thomas

 

[Le Basseur]

Hey folks,
I didn't saw the "Sowther"name,when you discussed about trafo's....did you all forget it?
My recent listening test showed that,without any doubt,won any Lundahl hands down!

 

[Brett]

Thomas,

I've not tried the other transformers, but that was not my point. The LL1680 allowed a lower DC bias which means one of two things
- you biassed the tubes lower, which changes how they sound, linearity, distortion etc, so it's not a direct comparison
- you saturated the core

Neither of these give a fair representation of what the trans can do. I'll be interested to hear of your results with the 1660/18

Le Bassuer,

Sowters have always intrigued me, but iron is too expensive to ship 12000 miles. Besides, I have a couple of local winders with excellent reputations I'm going to try soon. However, if you want to send me some, I'll happily try them out.

 

[fdegrove]

OPTS.

Hi,

My recent listening test showed that,without any doubt,won any Lundahl hands down!

Really?

They never had that good a rep in the past but what do I know?

Maybe economics wised up this long established British Empire company too?
It always takes them fifty years to notice a change in the world around them from their ivory towers anyway.

Cheers,

 

[James D.]

...OT - sorry...

Maybe economics wised up this long established British Empire company too?

Too true Frank.

I hear the British army is going back to the Enfield Rifle - this damm modern SA80 is no good...

If you want a bullpup done right try the FN90....

cheers

James

 

[siu sin man tho]

hi Brett,

if later U had time I hope U will try to consume a little bit of private time to test tango NP-126 pre-amp output.
For the cheaper product james, japan famous air tight also use their output trans.
I hope diyer had more choice.
I don't care to post one pair to U to test.
Is it very rare people in foreign area test or use tango or tamura transformers. James too.

thanks

Thomas