Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki 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

EL34 Baby Huey Amplifier
EL34 Baby Huey Amplifier
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 April 2019, 02:27 PM   #441
Francois G is offline Francois G  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Champaign, Illinois
Quote:
Originally Posted by bandol83 View Post
Hi Francois,
...
I put the schematic and the PCB in this message but it is still a work in progress therefor all remarks and/or suggestions are welcome... For info I made the PCB with the serigraph on the bottom side to facilitate the building

Rgds,
Marc
Looking at the schematic and PCB Im not sure how you are making the connections with the CFB coils on the output transformer. Did I miss seeing the connections?
  Reply With Quote
Old 20th April 2019, 05:01 PM   #442
Bfpca is offline Bfpca  Canada
diyAudio Member
 
Join Date: Feb 2007
Location: Nova Scotia
EL34 Baby Huey Amplifier
Marc, that is a very ambitious project! Good pla to go monoblock. I built a PPP kt88 stereo amp in 2001 and it weighs over 100lbs. I want to update that amp sometime soon, but it needs to get in line behind EL84 BH and possibly a balanced tube preamp.
When you build you should consider increasing your - bias supply above 100volts and also the current in the mosfet driver could be increased to help drive the extra capacitance and perhaps some grid current that may flow close to the 0 bias point. I find that I can see notches in the waveforms when driving high levels with the BH circuit with both el34 and KT88s due to the limiting of the bias supply and perhaps due to current limits. I noticed that even when I have notch free operation at the rated load impedance that the notches show up again if you lower the load impedance below the rated value.
I also found that the current sources in the output tube driver circuit were more linear when the 220k resistor was connected to the +bias supply (+22volts in my case) then when connected to the driver mosfet .
I am still fine tuning my BH and trying different operating points.
  Reply With Quote
Old 21st April 2019, 09:47 AM   #443
bandol83 is offline bandol83  France
diyAudio Member
 
Join Date: Nov 2004
Location: near Bandol, French Riviera
Hello Brian,

Yes, the Quad KT120 mono block will be about the weight of a stereo Baby Huey and that will be quite heavy already

I will also need two power supply transformer therefor the dual mono is a logical solution. For the Vbias, you are right, I already found that and recommended to reduce R39 from 33k to 15k, or even 10k, for the EL34 version. The -75V on the PCB is a reminiscence of the Baby Huey design In fact for this amplifier I will have a dedicated power supply board that will use a small 115 V AC transformer giving about -150 V DC for the bias. I still have not decided if I will use the attached schema or use the 50 V AC output of the Toroidy power transformer for the +Vdriver and use bridge instead of a single rectifier ? As I said it's a design in evolution and the attached documents are not definitive and not checked, many resistor values could be modified because I am using the duplicate fonction during CAD work and I check values at the end...

Your remark about the current source is interesting, may be it can be an improvement for the new project ?

Rgds,
Marc
Attached Images
File Type: png PCB Power supply TENA.png (297.3 KB, 115 views)
Attached Files
File Type: pdf Schema Power supply TENA.pdf (121.0 KB, 17 views)
  Reply With Quote
Old 21st April 2019, 09:54 AM   #444
bandol83 is offline bandol83  France
diyAudio Member
 
Join Date: Nov 2004
Location: near Bandol, French Riviera
Ooops, I put the wrong file

Sorry,
Marc
Attached Files
File Type: pdf Schema Power supply TENA.pdf (173.2 KB, 32 views)
  Reply With Quote
Old 21st April 2019, 12:40 PM   #445
Francois G is offline Francois G  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Champaign, Illinois
Quote:
Originally Posted by Bfpca View Post
I find that I can see notches in the waveforms when driving high levels with the BH circuit with both el34 and KT88s due to the limiting of the bias supply and perhaps due to current limits. I noticed that even when I have notch free operation at the rated load impedance that the notches show up again if you lower the load impedance below the rated value.

I am still fine tuning my BH and trying different operating points.
Brian, If I remember correctly, you have increased you bias supply to ~ negative 90Vdc on your EL34/kT88 build. Did you see those notches in the waveform with the designed negative voltage ~_75Vdc, or also at the new -90Vdc?

Could you clarify I noticed that even when I have notch free operation at the rated load impedance that the notches show up again if you lower the load impedance below the rated value. How do you lower the load impedance; change transformers? Or do you mean changes in speaker impedance at different frequencies?

Thanks for sharing your experience. Please keep us less technically-gifted builders informed of the results of your fine tuning.
  Reply With Quote
Old 21st April 2019, 10:18 PM   #446
Bfpca is offline Bfpca  Canada
diyAudio Member
 
Join Date: Feb 2007
Location: Nova Scotia
EL34 Baby Huey Amplifier
Quote:
Originally Posted by Francois G View Post
Brian, If I remember correctly, you have increased you bias supply to ~ negative 90Vdc on your EL34/kT88 build. Did you see those notches in the waveform with the designed negative voltage ~_75Vdc, or also at the new -90Vdc?

Could you clarify I noticed that even when I have notch free operation at the rated load impedance that the notches show up again if you lower the load impedance below the rated value. How do you lower the load impedance; change transformers? Or do you mean changes in speaker impedance at different frequencies?

Thanks for sharing your experience. Please keep us less technically-gifted builders informed of the results of your fine tuning.
Yes, Francois lowering the load impedance, in this case a power resistor, to a value lower than the rated impedance of the output tap. Specifically, I put a 4 ohm load on the 8 ohm tap and I got the notches back again. You see them near the top and bottom of the waveform. A small dip in the sine wave but not clipping I think it is when the output tube that is being turned off has a clipped grid waveform due to running out of - swing. If your -bias supply is not high enough it will cause this problem. I need to think about why it comes back when the load resistance is lowered. Remember that I am pushing the driver to its limits with my setup.
I am currently working on finishing the case for the BH. Busy with multiple projects and income tax and house renovations and...... etc!
  Reply With Quote

Reply


EL34 Baby Huey AmplifierHide 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
Baby Huey GB PCB - EL34 Build Thread spaceistheplace Tubes / Valves 11 8th October 2018 02:04 PM
FS: partially populated Baby Huey EL34 PCBs Abszero Swap Meet 2 18th June 2018 02:40 AM
First time baby Huey amplifier build mossmamc Tubes / Valves 131 21st November 2011 07:18 PM
Building the Baby Huey EL84 pushpull amplifier Bas Horneman Tubes / Valves 0 19th October 2009 08:21 PM


New To Site? Need Help?

All times are GMT. The time now is 04:27 PM.


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