4P1L PSE Amplifier for Sale!

Firstly, my apologies to all readers for not writing much over the last year. Things have gone a bit crazy between work and family commitments. Also, modular synthesiser work has taken a lot of interest lately to me. Finally, this blog was hacked twice and have been painful to get it back up again. Needless to say, I’m not an IT expert so I do the best I can!

Selling my beloved 4P1L

All good things come to an end. In this case, my loved 4P1L PSE Amplifier. I moved listening rooms with the growing family and space is now an issue. I no longer can store this beauty and I think it would be wise for someone else to enjoy it rather than collecting dust somewhere my attic (which is mostly full).

This amplifier gave me a lot of joy and sums up a “no-compromise” approach to DHT considering the design and component selection of the power supplies. It’s a very flexible beast as the power supplies (HT and LT) can be used in many different configurations – all the way up to a 300B and more.

The amp was originally presented here:

https://www.bartola.co.uk/valves/2017/02/05/4p1l-pse-amp-finished/

For the ones who remember my 814 amplifier, I reused the amazing power supplies which were feeding the 46 driver stage. The DHT filament raw supply is similar to these:

https://www.bartola.co.uk/valves/2012/12/29/4-65a-se-amp-46-driver-raw-supply/

One PS per channel (2 boxes on the right in the picture above)

It’s a no-compromise design here. Best custom-made JMS transformers designed to fit this amp supplies with split-bobbins and copper screening.

The HT supply is my design for 300B and 4P1L PSE. It has a lot of capacity which can be reused and is very flexible with its design. It has a surge protection start up circuit and two current meter (one per channel).

I will dig out the circuit and share all documentation for whoever buys this amplifier.

The amp use MM OPTs, 4mm plate machined by Schaefer. Filament bias and circuit as per own my design.

All cables provided.

4 valves selected and matched to gm and Ia by me with eTracer

You will need a preamplifier / driver – which isn’t included. Anything with gain of x8 will work (preferably a DHT stage like 01a, 26,4P1L, 2P29L, etc.) – this isn’t included.

This is “the one and only” Bartola 4P1L amplifier. It has gone back and forth to ETF.18 and got into quarter finals on the competition (personally and a few others think it could have gone further but listening levels and setup were not the best).

Needless to say:

No reserves
Payment upfront
Only collection in London, UK. No deliveries
Sold as-is. You need to know what you’re doing here 🙂

I haven’t got idea of what price to ask, need to think about it.

If you are interested, ping me.

Cheers,

Ale

DHT Supply PCB

I took me a couple of years but eventually found the time to build the BOM and a simple documentation guide for the DHT LT supply PCB. I’ve been using this PCB for a long time on most of my DHT preamps and in my current 300B SE Amplifier.

It’s a 16 x 8 cm board which can be stacked for a stereo DHT stage. Enough flexible is provided for all sort of filtering combinations (either choke to cap input supplies).

Some may say is a killer, but I add a common-mode choke to suppress HF noise from mains. I design my supplies with a no-compromise thinking and best possible components (e.g. including split-bobbin main transformers), chokes and capacitors to deliver the lowest noise possible to the filament supply.

This board doesn’t replace the filament regulator (e.g. Rod Coleman regulator), it’s just the raw supply circuit needed before them.

I will sell the remainder of my stock of these lovely ENIG finished PCBs. You can order them here.

300B SE Amp – here we go

A Brave New World

Surely you’re as tired as I’m with COVID-19. One of the best things I can do to distract my mind is to keep myself away from social media. Every stone you turn, there is COVID or a statement about it. I won’t moan as I have a job for now and a healthy family. Some members of my family were infected but nothing major. I can only say is that the world has change. And so my day to day life looking after the young family whilst working is a real challenge. Starting my fifth week of lockdown, I have to distract somehow my mind at times, otherwise will go mad.

A New Concept

Continue reading “300B SE Amp – here we go”

ER801a Driver Stage

Received the ER801a today back from Thomas. They were working fine, it was a faulty UX-4 socket pin of my tracer which annoyingly made the grid to appear faulty and open at certain voltage level. I need to replace it.

Either way, they are now in my system and I can only say how much I was surprised with the sound of these. They take the detail and timbre of the VT-25 to a next level. Amazing result, happy to have these as part of my driver stage. The preamp is the 201a feeding the ER801a into the 4P1L PSE.

Highly recommended valves, worth the price indeed.

46 driving 45 – SE Amp

My favourite valves together

Recently I revisited a beloved amp, the SE 45. This time I will share a more orthodox design without sand in play. Surprised? Well, I love lots of iron as well and here is a design I’ve been playing around for some time as I have all the components at hand.

Driving the 45

Continue reading “46 driving 45 – SE Amp”

814 SE A2 Amplifier

Goodbye 4-65a SE, at least for now

After enjoying the 4-65a SE amplifier for many months, I couldn’t resist myself from upgrading the output stage to the 814s. I just needed changing sockets and filament raw supply transformers to fit the requirements of this lovely transmitting valve. Needless to say, my recent tests on 814s were very encouraging. The 814 seemed to perform much better than the 4-65a in delivering 10W of class A2 sound at half the distortion levels. This to me, was only worth trying.

Continue reading “814 SE A2 Amplifier”

A collection of latest images

After upgrading my 26 preamp, turntable and adjusted the system to a great sounding state. Looking forward to play many records now…

HT power supplies

Latest System

26 preamp and 4-65a SE Amplifier

DHT filament supplies (and many of them)

26 and bigger brother 46

Reddish 4-65a

26 preamp Gen3

Lenco turntable

Setting up to play in the evening

4-65a SE Amp: testing it finally!

The much-awaited moment finally arrived. After yesterday’s driver tests, I did a lot of work this morning to assemble cables and test the output stage. What I clearly know now is that I won’t be needing any heating this winter! What on earth was on my mind when I decided to build this amp? God only knows…

Here are some pictures of the first tests in the workshop and then when I hooked it up to my system downstairs in the sitting room:

26 preamp and 4-65a SE Amp just before testing

Burning in the 4-65a!

Setting output bias

Measuring output

I did a quick measurement of the output THD without burning in the 4-65a or the amp. The operating point is not optimised but clearly shows a nice picture. First of all, the amp is absolutely quiet. The Rod Coleman regulators plus the extensive filtering on all supplies (LCLC and CLCLC) make this the quietest amp I’ve ever made! The distortion is higher than predicted. With the valves at 100mA/540V and with a non-inductive resistor load of 10Ω, the THD is about 2.7% for nearly 6W of pure class A power. Only 4% of the harmonic content is H3 and with a nice H2 component. The footprint of an SE amp is clearly on this amp.

Hooked it downstairs and after a lot of wiring I finally got to play some good records on this amp. I used my 26 DHT preamp. First record to be played was “a love supreme” (John Coltrane). Here are my impressions so far:

I’m surprised with the bass. It is powerful and not something I was used to in a single ended amp
Definitely needs some burn-in time. The amp improved after 1 hour of use
It’s loud! You can get 10W easily in class A2. Very loud for my room!
The tone is warm and very sweet. you get the sound of the DHT clearly
Dynamics are its forte. This amp responds very well to them

Some more pictures:

4-65a Amp finished

Cherry red anode!

First time up

A power supply madness!

Input transformers and 46 drivers

Now is time for proper listening after so much work. A real accomplishment and I’m feeling very proud. The amp fits within my cabinet so wife is happy 🙂

Listening to the 45 Single Ended (SE) Amplifier

A perfect and warm sound

Hard to describe in words what I felt when I played first time “Goodbye Pork Pie Hat” from Charles Mingus. Perhaps it was the due to the fact that I play saxophone, but inevitably for me this song is one of the best ones to test the response of any amplifier. Sax duets, solos, a great bass line and varied moods along the way can take the amplifier to their best of their abilities. Being a jazz fan, couldn’t help myself when listening this amplifier for the first time. I used to play an EL34 push-pull, and liked its sound and power – specially for rock. But when it comes to the first watt, this amplifier is breathless. Pure and a warm tone. Playing this song made me understand all the fuzz about single ended amps. But, far from opening the debate about that, I’m sure that a 45/46 in push-pull has its own merits and would probably will one of those amps I’d like to build in the future.

Having a FE167E full-range driver that have a relatively high efficiency (94dB/W), the 45 SE doesn’t sound low. It has its own personality. Brilliant for jazz, it may need a tad of power perhaps when playing some rock and classic stuff.

It took me some time to optimise the driver stage. Started with an SRPP, then a paralleled 6SL7 to an 6J5 loaded with a gyrator in mu-follower achieving less than 0.20% THD at 150 Vpp. A great driver in my opinion. Now need to replace the 6J5 for the lovely 7193.

It looks like a Frankenstein valve, but it’s a lovely thing to me. Many claim that it’s a superior valve compared to the 6SN7/6J5 or even CV1988.

Adding the 7193 will require opening my 45SE and not having music at home for some time so at the moment is not what I have in mind.

Perhaps when I get the 4-65A up and running? It will take some time for that…