845 Low voltage SE AMP - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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
Thread Tools Search this Thread
Old 16th July 2007, 08:16 PM   #1
diyAudio Member
Join Date: May 2005
Location: Como
Default 845 Low voltage SE AMP


I'm planning to build an amp with tha power of a 300b amp but with DHT 845 tubes.. I hope they are more economical and indistructible at this low voltages! Someone have build this amp?
I have some other low voltage schematics with845 to discuss...

Thanks in advance

Max ;o))

Click the image to open in full size.
  Reply With Quote
Old 17th July 2007, 01:02 PM   #2
nhuwar is offline nhuwar  United States
diyAudio Member
nhuwar's Avatar
Join Date: Jan 2007
Location: Cypress Texas
I could be wrong but I remimber people on this forum saying 845 dont like to low a plate voltage. But I could be wrong and I'm sure I will be corrected.

  Reply With Quote
Old 17th July 2007, 01:08 PM   #3
Tweeker is offline Tweeker  United States
diyAudio Member
Join Date: Dec 2004
Location: Cincinnati, Ohio
You wont be getting much power from an A1 SE 845 at low plate voltage.

A 6SL7 isnt going to provide very satisfactory drive to one, either.
Be sure your foil hat has a good low impedance ground.
  Reply With Quote
Old 17th July 2007, 02:32 PM   #4
MikeR is offline MikeR  United States
diyAudio Member
Join Date: Feb 2004
Location: Michigan
As most things in audio, opinions vary. I like the sound of a low power 845. I have a breadboard mono 845 that I am currently developing. Mine is at a little higher plate voltage, 430 volts and biased to 62 mA with a fixed bias supply similar to yours. I have a 4.8k transformer. Power is about 4 watts.

I do not use any feedback. I have also found that AC on the heaters works pretty well which suprised me since they are 10 volts.

My driver is a parallel 6SL7 also, but running as a mu stage using a constant current source. It seems to work pretty well. Looking at it on a scope, I get about 120 V p-p before distortion shows up.

Play around with the driver stage to find what you like. A simple 6SL7 SRPP also sounded good to me.

Do a search for Jim Doyle and 845. He studied low power 845 designs extensively.

Good luck.
  Reply With Quote
Old 17th July 2007, 05:03 PM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
kevinkr's Avatar
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Definitely take a look at mu stage and srpp drivers based on the 6SL7 running at around 2mA. Plenty of swing and good linearity, should be enough current available to get you a little beyond 20kHz allowing for C miller in the 845.

Definitely google Jim Doyle 845 project. I have heard a couple of low power 845 amplifiers and they sounded quite good, and know of one currently under construction. Power in the range of 2 - 5W is achievable at voltages below 500V.

I'm surprised to hear that ac heating at 10V worked ok, hasn't been my experience with 5V tubes, but who knows. I would heat these using constant current dc, (LT1084 based or similar) but quick and dirty AC may be ok depending on the particular set of tubes.

Linearity will be good enough that no global feedback should be required.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
  Reply With Quote
Old 17th July 2007, 10:37 PM   #6
MikeR is offline MikeR  United States
diyAudio Member
Join Date: Feb 2004
Location: Michigan
I ran across this link to Jim Doyle's web site. Lots of stuff here for low power 845 amps.

Jim Doyle
  Reply With Quote
Old 18th July 2007, 05:42 PM   #7
diyAudio Member
Join Date: May 2005
Location: Como
Hello to all and thanks for the interesting website!

what about this interesting link...


the amp shoul delivery about 11w with 750V an 5K load

Click the image to open in full size.

Click the image to open in full size.

I also read an interesting article on Italian Magazine CHF Costruire HI-FI that talk about possibility of Use 845 @ low voltages... if someone is interested I can ship some photos of the article....

  Reply With Quote
Old 18th July 2007, 09:50 PM   #8
Gluca is offline Gluca  Italy
diyAudio Member
Gluca's Avatar
Join Date: Nov 2004
Location: Back to Italy

I'd suggest to use a 813 (triode strapped). Much easier and cheaper than 845 and probably even better. There are talks here and there on this tube.

  Reply With Quote
Old 19th July 2007, 10:56 AM   #9
diyAudio Member
Join Date: Nov 2004
Location: Charlotte
I just recently converted my low voltage 845 amp from Direct Feed to Para-feed output stage.

I started out with 6EM7 driver that was in a Vacuum Tube Valley write up from Eric Barbour. He used it on a SV572 amp project.

I just created a -50v bias and had 490v on the 845 running on 85ma. I used that setup for about 7 years.

I needed the 6EM7 for another project and converted the amp to a SRPP using a 6SL7. This work surprising well considering the 6SL7 is not a hi current tube.

Last week I just converted in to Para-feed and is waiting for the new transformer to break in.

Once you get going, you can modify you amp to taste or if you are bored. If the new change does not work well, you can always change it back.

As they say: "It is the journey that is the reward"
  Reply With Quote
Old 13th January 2013, 06:56 PM   #10
diyAudio Member
MartinV56's Avatar
Join Date: Nov 2006
?????? DIY Audio Craft • View topic - 8W Low voltage 845 Single Ended Power AMP
  Reply With Quote


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Voltage sag JonnySwitchblade Solid State 6 8th July 2007 10:20 AM
Should I use high voltage value zeners or multiple lower voltage zeners in series? jarthel Parts 7 30th May 2006 04:56 PM
Rail Voltage to Capacitor Voltage Mermprin Parts 6 20th September 2004 03:56 PM
secondary voltage vs. primary voltage Stocker Parts 5 11th March 2004 07:41 PM
Rail voltage compared to transformer voltage SteveG Solid State 4 22nd July 2002 11:50 PM

New To Site? Need Help?

All times are GMT. The time now is 11:29 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2