EL84 Amp - Baby Huey - Page 41 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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
Reply
 
Thread Tools Search this Thread
Old 20th March 2008, 08:00 AM   #401
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Tim,
Food for thought. I'll think about this over the Easter 4 day break and post next week if I have any flashes of even mild brilliance.
Cheers,
Ian
  Reply With Quote
Old 1st April 2008, 04:11 AM   #402
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
I have just started the build process for my "Baby Huey". This is my fifth valve amp build, but the first this complicated, with constant current circuits. I think I am reasonably comfortable with wiring things up now, but would like to follow a step-by-step process of building and checking as I go. I have built the bias blocks and constant current sinks on perf boards with screw terminal connectors to make them modular, but was wondering if anybody could offer some advice on testing them. I would prefer to make sure they work before just connecting everything together and doing a "smoke test". As I am building this with a valve rectifier, I have built a small -15 volt regulated supply for the current sink (tested and working).

Any input/advice greatly appreciated!

Thanks,

Chris

CCS and Bias Blocks

Click the image to open in full size.

-15 volt supply

Click the image to open in full size.
  Reply With Quote
Old 1st April 2008, 05:49 AM   #403
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Chris,
These look good.
To test the -15V supply hook up a 1K resistor across the output and check that you have 15 volts across it. That won't check it to full capability but will give you a confidence test.

To test the diff amp current sources hook them up to the -15V supply you made and connect a dummy load of say 4K7 from the upper transistor cathode to 0V. Then check that you are developing approx 4.7V across the 4K7 (that is approx 1mA through the 4K7 dummy load).

To check the output tube cathode CCS (one at a time) hook it up across the -15V supply with the PS -15V to what would be the amp 0V connection and the PS 0V connection to what would be the amp cathode connection (to get polarity right) Then check for 0.6 to 0.7 Volts across the 16 Ohm resistor.

If you can be bothered I would be tempted to rebuid your -15V supply into a +/- 15V supply so that you can do the Yves (dupyv) mod shown in the top left corner of the schematics at post #369. This is just returning the 5K6 resistor (R1) in the EL84 CCS's to +12V (+15V in your case but its not critical) instead of wiring it to the tube cathode and the top transistor collector. Its not absolutely necessary but it will improve the stability of the CCS particularly under heavy drive of the amp - at the expense of requiring a +ve low voltage rail. Yves seemed to think it was an improvement and theory says he's most likely right.

I would not suggest you tackle his other mods but that one is relatively easy if you can be bothered redoing your -15V supply to +/- 15V.

Cheers,
Ian
  Reply With Quote
Old 1st April 2008, 06:24 AM   #404
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
Thanks for taking the time to respond Ian. I don't think I will bother with the +15 volt mod as I am building this amp while I should be doing uni assignments can't waste too much time... I will keep this in mind though for the next amp, as I am thinking of a PP 6L6 next, or I might mod this one in the future.

Thanks again, will keep posting as I progress.

Chris
  Reply With Quote
Old 1st April 2008, 09:05 AM   #405
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
Thanks Ian,

Your assistance helped me to identify a minor wiring error in one of the bias blocks. Managed to fix it without damage to any of the components.

All Bias Blocks are reading 6.4 volts (I am using 18R resistor as I expect a B+ a little on the higher side).

CCS for the input triodes are reading 6.8 volts across a 4K7 resistor. This works out to 1.45mA, a little on the high side. My question, is this OK? Looking at the ECC83 curves it looks like 170 volts and 1mA are -1.5v, while 1.45mA will place it at about -1.1v.

Should I leave as is or any suggestions to adjust?

Thanks for the ongoing help!

Chris
  Reply With Quote
Old 1st April 2008, 04:31 PM   #406
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
Hmmm,

Feel like a bit of a dill. Was wondering why the different result than expected from the CCS. Noticed that the LEDs were not lighting. I had them wired backwards

Re-wired. LEDs light, voltage reading is 6.03v which works out to 1.28mA. Not quite 1.0mA, but closer than with incorrect setup. Hopefully this is close enough now.

Cheers,

Chris
  Reply With Quote
Old 1st April 2008, 08:25 PM   #407
jazzbo is offline jazzbo  Canada
diyAudio Member
 
jazzbo's Avatar
 
Join Date: May 2007
It's the voltage drop across the LED's diode junction minus the base-emitter drop of the BC547/549 that sets the voltage, and hence the current, across the 1Kohm resistor. There will be some variation in the LED forward voltage drop between LEDs as well as variation due to current through the LED. There will be some slight device-to-device variation in the base-emitter voltage in the '547/549s as well. You could breadboard and match LED/transistor combos or change the 1K resistor to a 1.1 or 1.2K and put a trim pot (say 20K) across it, if you want to be anal about achieving exactly 1 mA. All that being said, I don't expect that the 1.28 mA will be a problem. The CCS as designed is rather temperature sensitive anyway so you won't know what the final actual current is until it's in the amp and warmed up.
  Reply With Quote
Old 1st April 2008, 09:25 PM   #408
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
Thanks jazzbo.

Appreciate you taking the time to explain that. I am just glad that I was able to test, trouble-shoot and repair before putting them in the amp

Chris
  Reply With Quote
Old 2nd April 2008, 10:08 AM   #409
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
I have started the construction. Most of the chassis work is done, just have to drill the back panel for the speaker binding posts and drill hole in front panel for the power switch. Hope to start wiring tomorrow. Want to do the filament wiring first, but have run out of single core of sufficient gauge.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
  Reply With Quote
Old 2nd April 2008, 02:31 PM   #410
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
Most of the components in place, just need to purchase one more tag strip and some speaker binding posts. Start wiring tomorrow. Here is under the hood so far...


Click the image to open in full size.
  Reply With Quote

Reply


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
Red Light District/Baby Huey (EL84 P-P) Output Iron dsavitsk Tubes / Valves 3 14th February 2009 02:21 AM


New To Site? Need Help?

All times are GMT. The time now is 05:20 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2