Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Russian rod tubes in a battery all-tube mini amplifier prototype
Russian rod tubes in a battery all-tube mini amplifier prototype
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th June 2018, 08:46 PM   #1
Thomasha is offline Thomasha
diyAudio Member
 
Join Date: Jun 2012
Default Russian rod tubes in a battery all-tube mini amplifier prototype

Hi, working on a new subminiature amp!
The circuit is a PP 1j29-b power amp, with 1j24-b preamp and PI.
The OT is a line transformer (10W, 100V, with the 0.625W tap, which should give a 29k primary when using the 4 ohms input with my 8 ohms speaker).
The windings are a little off. I measured 220 vs. 251 ohms from the center tap to the anode connections.

Here is the first draft, with some voltage readings:
Click the image to open in full size.

I tested the concept in a turret board, here are some pictures>
Click the image to open in full size.
Here you can see the PP stage, two 1J29B (1SH29B) tubes, the 10W transformer, the two batteries and the SMPS.

Click the image to open in full size.
Here is the whole thing, with lots of cables, during the debbuging.

Click the image to open in full size.
Click the image to open in full size.


Please, take a special look at this suppressor driven PI...
I'm not sure if it is working right, it looks kind of out of balance when using my cheap oscilloscope. I don't know how I should design this, other than using the information available here:
Phasendrehstufe mit Verteilungssteuerung

For the high voltage I'm running a MAX1771 SMPS using 2 Li-Ion batteries (which converts from 7.4V to 100.6V). The same batteries are also used for the heaters, where after some tricks I could get something like 32mA at 4.8V (in my case using a 5V regulator).

And a small sound test with a small 4" speaker on the table (no cab, so a little too bright)>
YouTube

It still has some problems, as:
-Blocking distortion with gain maxed
-Motorboating with volume maxed
-A lot of noise (long cables used in this prototype)

To conclude, I think this proves the concept, I just need to fine tune it. I think with a proper board I can test it without all the noise.

If someone has some experience with designing pentode gain stages, or even the PI, please step in!

Last edited by Thomasha; 22nd June 2018 at 11:06 PM.
  Reply With Quote
Old 21st June 2018, 03:01 AM   #2
thoglette is offline thoglette  Australia
diyAudio Member
 
thoglette's Avatar
 
Join Date: Dec 2008
Quote:
Originally Posted by Thomasha View Post
If someone has some experience with designing pentode gain stages, or even the PI, please step in!
Firstly, congrats for doing what some of us () have been gunna do for years.

Secondly, somewhere in my pile of PDFs I'm pretty sure I have some triode wired curves for these tubes. You have the option of moving these to triode mode and dropping the gain. And more easily echoing "normal" amp design practices.

Thirdly, Valve Wizard has a great article on Pentode design. Also in pentode mode you've got buckets of gain and probably don't need anything like the number of stages you're using.

Fourthly, motorboating is inevitable with that design. The golden rule is "no more than two stages on the one cap". See also the usual causes of buzz and much. Put another RC dropper onto the first valve; drop the gain of that stage (by triode strapping) and most of your problems should go away.

Fifth: there are some real challenges with getting DHTs heated and setting the bias. There are some old circuit diagrams around for hand-held radios using these tubes which have some examples. Also have a look what the guys in the "lunatic fringe" of DIY HiFi are doing (e.g. this thread) as they know how to get the best out of DHTs

Finally, blocking distortion indicates grid current. You can either limit the voltage excursion/gain; use ITs; drop your coupling cap values and pad between stages (like a JCM800) or use really big grid stoppers (e.g. per the Soldano)

Last edited by thoglette; 21st June 2018 at 03:08 AM.
  Reply With Quote
Old 21st June 2018, 03:12 AM   #3
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
I love it, a truly unusual project!

I don't know enough about DHTs or Russian rod pentodes to be helpful with the design, but I'm in your corner, cheering for you to succeed.

-Gnobuddy
  Reply With Quote
Old 21st June 2018, 04:17 AM   #4
thoglette is offline thoglette  Australia
diyAudio Member
 
thoglette's Avatar
 
Join Date: Dec 2008
I need to rustle through some files that are packed away but meanwhile some bookmarked links I've found useful which refer to triode operation.
Summary Russian Rod Pentodes
Russian Rod Pentodes 1 – Valves or Tubes
https://www.edn.com/electronics-blog...sian-rod-tubes
They also remind me that these can be good for up to 200MHz so you want to dump any gain over 10kHz or it will sing like a bird
  Reply With Quote
Old 21st June 2018, 08:12 PM   #5
Thomasha is offline Thomasha
diyAudio Member
 
Join Date: Jun 2012
Thank you guys for the comments,

Today I fixed some mistakes and checked the gain of each stage. What is really interesting is that I was heating the 1J29B with only 1,4V at the 2,4V configuration and they were still working. The current was also really low at the heaters. By removing the 5v voltage regulator I got a really strong signal, it is much louder now.

After checking the gain stages I already identified that there is too much gain, it already distorts after the first stage. Only by reducing the volume of the guitar and the gain at the same time I could get some clean.

Another problem is the lack of balance of my PI. One side has a gain of 2,5 against a gain of 6,7 at the other. What I find weird is the fact that the plate is at only 14V while the screen grid is at 48V. I'm missing something here, could be something to do with the grid, which is at 2V.
I could remove one gain stage and make a normal PI, which would have a better balance than this one.

I will read a little more about the tubes. I started using Valvewizards book, but the datasheet that I found is for a screen voltage of 45v and I'm running it at 92V. So I tried the paint_kip to trace the pentode curves and just increased the screen voltage hoping that the resulting curves are something near the real case.

There are some measurements of this tubes over radiomuseum, but again at lower voltages. Interesting is that they show a 1J24b circuit with screen feedback, which should be a triode mode with higher gain (think they managed to obtain up to 100, if I'm not wrong). Maybe I give it a try.
  Reply With Quote
Old 22nd June 2018, 01:38 AM   #6
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
Hard to comment when the schematic is so small and can't see any values.
  Reply With Quote
Old 22nd June 2018, 07:48 AM   #7
Thomasha is offline Thomasha
diyAudio Member
 
Join Date: Jun 2012
I increased the size of the image. When it's an imgur link the last letter of the link corresponds to the size, by removing the "l" the image can be seen in original size.
  Reply With Quote
Old 22nd June 2018, 02:19 PM   #8
thoglette is offline thoglette  Australia
diyAudio Member
 
thoglette's Avatar
 
Join Date: Dec 2008
Quote:
Originally Posted by Thomasha View Post
Another problem is the lack of balance of my PI. One side has a gain of 2,5 against a gain of 6,7 at the other. What I find weird is the fact that the plate is at only 14V while the screen grid is at 48V. I'm missing something here, could be something to do with the grid, which is at 2V.
I know it's late but I just can't get my head around that PI
  Reply With Quote
Old 22nd June 2018, 10:28 PM   #9
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
I have been trying to analyses it, not as far as actual voltages but just how the damn thing works. I just sort of go around in circles without getting it. Mind you it was only a couple of minutes so far but I can say having the schematic larger doesn't help all that much.
  Reply With Quote
Old 22nd June 2018, 10:48 PM   #10
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by Printer2 View Post
I just sort of go around in circles without getting it.
Well, that makes three of us now. I don't get it either.


-Gnobuddy
  Reply With Quote

Reply


Russian rod tubes in a battery all-tube mini amplifier prototypeHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Russian UHF amplifier tubes thomasweissbach Tubes / Valves 13 1st March 2018 02:55 AM
Tube SE amplifier with 6P3S (russian tube) danzup Tubes / Valves 48 6th June 2013 05:51 PM
NOS Capacitors(russian, phillips), Russian tubes, SS amp kits, power TX rvrazvan Vendor's Bazaar 0 26th May 2011 05:32 PM


New To Site? Need Help?

All times are GMT. The time now is 09:37 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki