My new all DHT amplifier

[Rajiv]

Hi,

Posting some pictures of my new all DHT amp being built by Viren.

The amp uses the Russian 4P1L tube. The transformers and chokes are Partridge. It is all 4P1Ls, configured as triodes, with an input/driver triode through an interstage transformer splitter, to push-pull triodes. No global feedback at all. Output power about 4 watts.

My interest in the little known 4P1L tube grew after I got the Lyrita DHT pre. The sound of this tube when used as a triode connected using filament bias as Viren does in his DHT pre is magical.

I started reading up on this tube and came across these threads on DIY audio.

One more 4P1L SE - diyAudio


#26 pre amp - diyAudio

I called up Viren and asked him if he could build one 4P1L based amp for me. Viren too had been following these threads and said yes . I had a spare set of Partridge output transformers and Chokes that were right for a push pull 4P1L amp.

Initial reports from Viren about the sound "It's playing very well - still has to break in as far as the caps go. If I were to use one word to describe the sound - it's "beguiling"! It charms you by drawing you into the music right away. There's a sense of rightness to everything, an ease with which the music flows. Slightly laid back, but that may improve with better resistors in the DHT heater supplies. There's something magical in voices reproduced through it."

The amp will be with Viren for some more time for more tweeks/changes . FM's can drop by at Viren's(at Viren's convinence) home for a listen to this amp.

Thank you Viren for building me the amp and putting up with my telephone calls at all odd hours and my often silly questions/doubts.

Regards
Rajiv

 

[apk]

Congratulations! Have always been fond of Viren's creations.

After Prem, you are the second person to get a custom amp made through Viren.

Will you be connecting this with Viren's DHT pre-amp?

Regards,
APK

 

[srinisundar]

Yes, DHT pre gives an clinical pure sound and love to hear this DHT amp with DHT Pre

Will this be available for the meet for 10th March, 2013 ?

Regards

 

[Rajiv]

Hi,

This is an integrated amp. No pre -amp needed.It uses the same tubes as the DHT pre.

No, Srini the amp will not be available for the meet on 10 March. Still some fine tuning/tweeking to be done.

Regards
Rajiv

 

[viren bakhshi]

Just a small writeup on the circuit design for this amp:

It's a two stage amplifier - input gain stage also acting as a driver for the output stage, which is push pull. The phase splitting is done through an interstage transformer with a centre tapped secondary winding. The overall design was to use the wonderful Partridge output transformers, and chokes, that Rajiv had.

Of course, the raison d'etre of this amp is the Russian directly heated pentode 4P1L. There aren't many cheap DHTs available, and this one excels in linearity when connected as a triode. It's used that way in both stages of the amp. A measure of that is, even in this push pull amp, a level of clarity with no feedback used at all.

An innovative aspect that this tube allows is the use of filament bias - the voltage drop over a resistor inserted in the heater circuit, that sets the bias and operating point of the tube. Each tube then uses an independent DC heater supply which also sets the bias of that tube. This eliminates large bypass capacitors, and, so, none of their sonic evils.

The amp has low overall gain, and is suited to line sources with a healthy output (2V). Since the max output power is about 4 watts/channel, you should have high sensitivity speakers to go with it. That is no problem for Rajiv!

It's very difficult to put in words the experience of listening to music through a good system. This amp helps you feel the music as its meant to be. You have to listen, to experience what the term "musicality" really means!

Regards,
Viren

 

[stevieboy]

Hi Rajiv,

Congratulations this should be a good addition to your store of vintage goodies. Will await your impressions. I can imagine it mating very well with the Altecs.

Regards

 

[captrajesh]

Posting some pictures of my new all DHT amp being built by Viren.

Whoa Rajiv, how missed the thread!!!

You must be awaiting eagerly. Any developments?

 

[anilva]

Rajiv,

One of the things missing in my collection is a good tube setup. I know you have been suggesting a DHT based attempt. Your posting is tempting me to try tubes sooner than later.

Will listen to your system whenever it is ready.

Cheers.

 

[Beast_of_burden]

After the 4P1L, which is reportedly better than the 2A3, can you go back to the 2A3 SET? Does the 4P1L annihilate the 2A3? 4P1L supposed to be extremely microphonic, how has this problem been dealt with?

 

[lifewater]

Congratulations Rajiv. One more beauty from the stable of Viren Sir. I can only drool thinking about the sound.

Regards,

Lifewater

 

[Rajiv]

Hi,

After the 4P1L, which is reportedly better than the 2A3, can you go back to the 2A3 SET? Does the 4P1L annihilate the 2A3? 4P1L supposed to be extremely microphonic, how has this problem been dealt with?

I have been listening to the 4P1L amp these past few weeks, and it sounds very good.

I would not say that the 4P1l is better than the 2A3,just different. The 4P1L is closer to the 45 in sound signature. It is a leaner sounding tube and does not flesh out the mids like the 2a3. I would like to mention that I have not heard a "real" 2A3 tube i.e. I am only comparing it to the 2A3C tube which is a 300B with a 2.5 volt filament.

Both the 2A3 and 4P1l amps are very musical and I can easily live with either of them. Good sounding audio products do not annihilate each other they present music with their own unique flavours. I like the musical flavours of both the 2A3 and the 4P1L amps and am lucky to own both.

All credit to Viren for designing these superbly musical amplifiers.:clapping::clapping:

I have not had a problem with microphonics with the 4P1L tube in the DHT amp,but in the DHT per the tubes would tend to go microphonic when they were new,but now after they have broken in I do not have any problem with microphonics.

Regards
Rajiv

 

[Beast_of_burden]

Hi Rajiv,

Is your 2A3 tricked out like this 4P1L with special transformers et al? I was checking prices for transformers from Sowter, Lundahl, etc - pretty expensive I must say.

 

[Rajiv]

Hi,

Hi Rajiv,

Is your 2A3 tricked out like this 4P1L with special transformers et al? I was checking prices for transformers from Sowter, Lundahl, etc - pretty expensive I must say.

The 2A3 amp. uses the stock Delta transformers.

Regards
Rajiv

 

[Beast_of_burden]

How did you snag these partridges? I am sourcing Magnequest OPTs for the Lyrita 2A3. Can the power and interstage transformers be improved upon?

mQ iron seems to be the easiest to source at a reasonable cost. Please advice on other transformer choices for the 2A3.

 

[Rajiv]

Hi,

[QUOTE. Can the power and interstage transformers be improved upon?

mQ iron seems to be the easiest to source at a reasonable cost. Please advice on other transformer choices for the 2A3.[/QUOTE]


The Partridge transformers came from another vintage amp that I picked up a while ago.

There will not be a cost effective improvement changing the stock power transformer in the Lyrita 2A3 amp,but using better interstage , OPT's and maybe chokes( you will need to ask Viren about the chokes)will certainly be worthwhile.

You should consider the Hashimoto interstage and OPT's for your amp. The interstage transformer is as important as the OPT.

The standard Magnequest transformers may not be a big improvement over the stock Lyrita transformers,but their nickel core ones which are more expensive should be good.

Regards
Rajiv

 

[GeorgeO]

I have Magnequest output trannies for one of my amps. They have a wide range of trannies and are well regarded.

 

[Abszero]

Just a small writeup on the circuit design for this amp:

It's a two stage amplifier - input gain stage also acting as a driver for the output stage, which is push pull. The phase splitting is done through an interstage transformer with a centre tapped secondary winding. The overall design was to use the wonderful Partridge output transformers, and chokes, that Rajiv had.

Of course, the raison d'etre of this amp is the Russian directly heated pentode 4P1L. There aren't many cheap DHTs available, and this one excels in linearity when connected as a triode. It's used that way in both stages of the amp. A measure of that is, even in this push pull amp, a level of clarity with no feedback used at all.

An innovative aspect that this tube allows is the use of filament bias - the voltage drop over a resistor inserted in the heater circuit, that sets the bias and operating point of the tube. Each tube then uses an independent DC heater supply which also sets the bias of that tube. This eliminates large bypass capacitors, and, so, none of their sonic evils.

The amp has low overall gain, and is suited to line sources with a healthy output (2V). Since the max output power is about 4 watts/channel, you should have high sensitivity speakers to go with it. That is no problem for Rajiv!

It's very difficult to put in words the experience of listening to music through a good system. This amp helps you feel the music as its meant to be. You have to listen, to experience what the term "musicality" really means!

Regards,
Viren

Hi Viren,
I just registered on HiFiVision. Browsing the web today for Russian DHTs I found this thread. Congratulations for your creation. I am also very fond of 4P1L and I have my latest incarnation of a sterea pushpull with quad 4P1L at simplepleasuretubeamp.com.
I experienced the same pleasure to the sound of this direct heated pentode triode strapped. I never had the chance to listen to a 2A3 so I cant compare, but the sound of 4P1L is superb and it is worthed to experience with it. In my setup I used all Lundahl transformers and Rod Coleman excellent filament regulators.
I used a 6N30P as driver and love the sound of this combination. I am working right now on a SE with all DhTs using 4P1L. Indeed using same tube for both final stage and and driver one needs 2V to get full power. I like the sound of the SE even better than the PP. Indeed 4P1L is a bit microphonic, just needs a lot of attention when designing the mechanical of the amplifier. Needs a good antivibration solution. I would look into Thomas Mayer ideas forthis purpose.
I am sorry to reply to an old thread, but I thought itwould be useful forsomeone who is interested in building with4P1L.
Best regards,
Radu

 

[viren bakhshi]

Hello Radu,

Good to hear from you.

Yes, lots of interest in this DHT from do-it-yourself guys. I'm happy that you are enjoying the sonics of the tube also. I'm certainly not done with this tube - have some design ideas that I need time to pursue.

Regards,
Viren