With a quick mod on one of my active preamps, I managed to implement very quickly the 6Э6П-ДР (6e6p-dr) driver in my system. Here is how the circuit looks like:
The bias point is good enough for driving a 4P1L PSE stage. You could push it up to 200V, but not really needed. I’ve discussed this valve and its performance in my previous post.
Regarding the filament circuit, I have at hand a 15VDC raw filament supply for my DHTs. I put the filaments in series and used my own LDO LV regulator which has a slow start feature and its very low noise. The cathode-heater insulation of the 6e5p proved to be poor so this valve isn’t the best for AC heating. Just as a precaution measure, the regulator would prevent any supply noise to filter into the circuit.
The result is fantastic. I thought the gain could be too much, but is perfectly fine for the 4P1L PSE output stage. I’d implement this driver instead on what I proposed earlier in this post.
The harmonic profile is really good, see below:
My first impressions are great. I always loved the sound of this IHP. It’s one of my favourite drivers as I said before and blends really well with the 4P1L PSE.
You will probably don’t want any more gain. This is good enough and will drive the 4P1L PSE at maximum power easily. If you implement a 3-valve version of the PSE design, you’d enjoy the extra power. I would recommend adding a source follower in such a case and implement fixed bias.
I’ve decided to make something similar using 6e5p and a follower and adding a switched attenuator and removing my preamp/ driver stages from my power amplifiers. Just output stages, 6e5p can drive all my output stages, 4p1l, 300b, gm70 and 833 so no point replicating.
Hi Enzo, agree!.
If you can find 6e6p-dr please try them, they are better than the beloved 6e5p!
Nice thing on the blog now is that you can upload your images in your comments! I like that 🙂
This stage sounds really nice. It doesn’t have the DHT detail, but sounds fantastically well. I really enjoy playing this, the dynamics are there and good overall response.
I will experiment with different cathode resistor types and see what is the impact in the overall sound
DHT driver are often overrated in forums, i like 46 as driver but you need a stepup transformer, i have also tried the 6E5P and finally use an E55L very good as driver or spud amp .
I appreciate your point of view, however I don’t agree entirely. I don’t think DHT drivers are overrated. Their sound is unique, but agree they are hard to implement. You need a SUT and many are hard to implement with filament bias, like 46 or 45 (Even 50). When you factor in the complexity of their filament supplies, yes a lot needs to be done just for a driver.
I implemented the 46 in filament bias (yes, absolutely crazy idea) and was worth the trouble. In hindsight, I won’t do it again simply because the resulting system is huge in space and generates a lot of heat!
I never tried the E55L but heard many good things about it. It’s expensive these days though. The 6e5p or (even better) the 6e6p-DR is a fantastic valve which still is affordable.
If more gain is needed, 6j49p-DR, 6j52p-DR (or D3a) with 12HL7 are my preferred choices these days.
Hi Ale,
I’m gonna try this preamp/driver today but in a long differential pair approach (and with some cathode degradation). What CCS tail would you suggest? I’m thinking of Jones’s cascoded BJT CCS with LED or zener voltage references.
Best regards from sunny Dublin 😏
Silviu
Hi Silviu
Good shot. I have a CCS PCB based on cascoded MOSFET/FET that would work great. Also the bipolar version is very good. I’d suggest trying it out without CCS and a simple resistor. If the anode load is a gyrator then fine, otherwise you will have a “fight” between CCSs and you should make one stiffer than the other (e.g. anode versus tail). Read Morgan Jones’ book about this topic if you haven’t done it so far.
Dublin, what a great city. Haven’t been there for a while. Next time we shall go for a Murphy’s stout, ok?
Good luck!
Ale
You are refering to the 4th edition? (I did not get it yet)… you can leave a mail to savu_silviu@hotmail.com anytime you are in Dublin
Hello Ale,
When using high Gm valves, such as the 6e6p-dr, where you must use ferrite beads in each of the pins, except the heater, do you have a recommended part number with the correct frequency range to attenuate? More specifically, which ferrite bead part number do recommend to suppress oscillations when using the 6e6p-dr? Would a 6 hole bead such as the Würth WE-UKW Series 6 hole bead, part number 74275042 (https://www.mouser.com/datasheet/2/445/74275043-1696159.pdf) suppress a wide enough frequency spectrum (from 1MHz to 100MHz) to be effective?
Best regards,
Paul
Hi Paul
I’ve been using these with great results for years:
cheers
Ale
Hello Ale,
It looks like the URL to the part number did not make it into your comment above. Could you please repost the ferrite bead part number that you had in mind?
Thank you very much!
Best regards,
Paul
Hi Paul,
This is the link, hopefully it comes ok now: https://www.mouser.co.uk/ProductDetail/875-28L0138-50R-10
https://www.mouser.co.uk/ProductDetail/875-28L0138-50R-10
cheers
Ale
Hello Ale,
Thank you! The URL came through perfectly this time.
Best regards,
Paul
Hi Ale,
I am concerned about the 500 hour life spec for the 6E5P, although many have had results indicating that it is overly conservative and have handily exceeded 500 hours. The 6E6P-dr is spec’d at 10000 hours so is much more appealing, but there are no traced characteristics or values of mu, Ra and gm for it triode connected. From your experience with it, is it close enough to 6E5P to be a drop-in replacement?
Also, I have zero experience using ferrite beads but I have seen admonitions about their use cautioning to keep them from touching the socket tags and to fix/glue/epoxy them in place. Can you amplify further how to do those things? Seems a daunting task, to the extent that some folks fall back to just using resistor stoppers (which have their own problems re fixing them in place. It’s good to see the reference to specific PNs and sources here, but some additional tutorial would surely be helpful.
As usual, many thanks for your efforts and Best Regards,
Robert
Hi Robert
I used both valves with great results over the years. The main challenge with these valves is that parameter variance is considerable. I settled over the years for the 6e6p-dr as my preferred one. I have plenty in stock and never bothered about their lifespan. Never had to change one valve so far.
I will upload latest curves I posted so you can used them
Cheers
Ale