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.

12BK5 Hybrid Amp
12BK5 Hybrid Amp
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 2nd January 2019, 03:03 PM   #1
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
Default 12BK5 Hybrid Amp

I have enough projects waiting for me to work on and I am not short on amps but I really need to build a new one. I have not used the 12BK5 and I have a bunch of NOS ones collecting dust. I am hoping that I can get them to play nice with a MOSFET phase inverter, 70V line transformer, a laptop power supply and a switching high voltage module.

Click the image to open in full size.


The 12BK5 biases up at -5V in single ended duty so it does not need a lot of signal prodding it so I might get away with a single 12AX7 with a Bassman styled tone stack.Whether the negative feedback remains depends on the amount of gain and the low end through the output transformer.I have used the IRF830 for the PI so I know that part will work, will be trying the LND150 to see how it will do.
  Reply With Quote
Old 2nd January 2019, 08:11 PM   #2
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
Nothing fancy, may give it a shot of paint later. To sit in a Tweed type of cabinet, maybe with an 8-10" speaker.



Click the image to open in full size.
  Reply With Quote
Old 3rd January 2019, 10:15 AM   #3
Thomasha is offline Thomasha
diyAudio Member
 
Join Date: Jun 2012
Nice one!
It's already a nice chassis. Love that you used a SMPS.

This tube is really nice, 3.5W in SE. The filament current is a bit high at 12v though.

How high is your plate voltage? Can the SMPS really supply the expected 80mA?
  Reply With Quote
Old 3rd January 2019, 03:40 PM   #4
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
We will see what it can do. Part of the reason for this build.
  Reply With Quote
Old 10th January 2019, 04:55 AM   #5
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
No NFB for now, need to update part changes but I think this will be the board.


Click the image to open in full size.
  Reply With Quote
Old 26th January 2019, 08:44 PM   #6
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
Finally found the board again, looked for it all over the house. Here is the board without the messy wires going places. Mounted the sockets and added the screen and grid resistors.


Click the image to open in full size.
  Reply With Quote
Old 27th January 2019, 12:07 AM   #7
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
Bought a tabletop radio today for $20. It is a battery operated one, 1R5, 1T4, 1U4, 1U5 and 3V4 tubes running 8.4V heater string at 50 mA, 90V plate supply for 0.25W. The 1U4, 1U5 and 3V4 are all pentodes and look like they may be an interesting project. I thought a 5W SE transformer for this cabinet and a 6x9 speaker might be useful.



Click the image to open in full size.


Seems someone thought the same thing with the speaker and it looks like they upgraded the output transformer. Thinking about it and looking at the wires, it might be a line powered version and the tube complement would have been a more common configuration.



Click the image to open in full size.


I think I see a pattern why it takes me a while to complete projects.

Last edited by Printer2; 27th January 2019 at 12:10 AM.
  Reply With Quote
Old 27th January 2019, 07:55 PM   #8
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
So much for working on the 12BK5 amp, cleaned up the radio for future consideration.


Click the image to open in full size.


Going to see if I have any available seven pin tubes. I never expected to do a whole amp with them so I didn't stock up. As an idea.


Click the image to open in full size.


I expect the volume and master volume will go in the volume and tuning positions and a input jack as well as treble and bass controls in the tuning window on the plate.
  Reply With Quote
Old 29th January 2019, 05:08 PM   #9
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by Printer2 View Post
Nothing fancy, may give it a shot of paint later.

Click the image to open in full size.
Is that a length of steel C-purlin as used in building construction? ( Purlin C






- Purlins and top hats Supplies











| Steeline
)

Might I ask what you used to cut it so cleanly? Cold saw? Band saw? Something else?

There was a construction project right next to my work place, and when it ended, the workers thoughtfully abandoned a pile of construction rubbish right outside the side door of the room where I work. Buried in between scraps of drywall, dozens of loose nails, and chunks of thermal insulation, I found a couple of short lengths of steel C-purlin, which I rescued and saved for possible use as chassis.


-Gnobuddy
  Reply With Quote
Old 30th January 2019, 01:39 AM   #10
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
I grabbed some C-purlin once, have it around here somewhere. No, this is just a scrap off cut from work. We have a small metal working shop at work. So just a shear and brake for this one. There will be wood blocks in the ends to which the screws that hold the chassis in the cabinet fasten to. So it will be fairly sturdy. This galvanized sheet is a little stronger than what homes have, can't remember the gauge.

I did a photo example of cutting and bending a similar chassis at one time, probably still at Photobucket but I still have issues with them so won't be visiting there soon. The thickness is still thin enough to cut with a hand sheet although it takes some effort. Can cut it with a fine blade hacksaw or a bandsaw if you have one. Scribe a line and with a file you can get an edge that would not be much worse than done with a sheer. I showed how to bend the metal using some angle iron and bar stock along with a piece of wood and a hammer. The more patience you have and going slow creates a better look than a get the job done style.

The chassis pic with the sockets mounted has a piece spot welded in where I had a hole for a socket and now the output jack. I thought it was a better arrangement, I won't be having speaker magnet issues. I am thinking of wiring it up tonight or tomorrow. That or my Telecaster project. The guitar will be more useful to me, the amp is just something I wanted to do because I have not done any electronic project for years. Just a cheap and dirty project to scratch an itch.
  Reply With Quote

Reply


12BK5 Hybrid AmpHide 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
Hybrid amp kees52 Tubes / Valves 152 12th February 2019 07:21 PM
12BK5 UL tracing gone boosted triode? avincenty Tubes / Valves 3 12th March 2012 03:58 PM
OB 3-way Hybrid ctrevith Multi-Way 16 27th March 2009 11:25 PM
the hybrid one arhi45 Tubes / Valves 11 8th May 2007 09:44 PM
My wacky idea for a hybrid horn loaded woofer/planar widerange hybrid loudspeaker. Spasticteapot Multi-Way 0 30th November 2006 05:16 AM


New To Site? Need Help?

All times are GMT. The time now is 02:14 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki