EZ125 Quad KT88 Project - Page 2 - 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 22nd May 2013, 01:31 AM   #11
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Audio research at 12k, seems a bit pricy, but I guess it's all relative. My question on the tube spacing is that something that I should really worry about if I'm running the amp at human listening level, ie, for 4" spacing on the tubes for full dissipation, can I assume a derating of continuous power but be ok it planned operation is not at full till.

$12k amp catching on fire, guess they should ship it with a halon system. BTW I solved the leaving the amp on problem somewhat by having them plugged into a GE mechanical timer Well doesn't really solve the problem, but helps some.

Thanks for spurning the ideas and raising issues.

Sandy
__________________
Working on electronics www.EZ260.com and cars www.GTSparkplugs.com
  Reply With Quote
Old 22nd May 2013, 02:14 AM   #12
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
I tried to talk that guy out of buying it but he has more money than he knows what to do with so he did not listen
  Reply With Quote
Old 22nd May 2013, 02:23 AM   #13
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
I also seriously think that guy's wife married him for his money as they bicker and demonstrate all the classic signs of emotional immaturity. This tale just makes me work even harder at bettering myself in my field. Knowledge is power, not the rich bitch wanting the latest designer fad

By the way, the spacing I believe is critical. Even at normal levels, on a push pull quad the heat can be felt 3 feet away. On summer days, the amplifiers alone raise the ambient temperature to where I need my air conditioner. That is a normal 27 degree summer day. Imagine the heat between the tubes. Yikes!

Last edited by BRSHiFi; 22nd May 2013 at 02:28 AM.
  Reply With Quote
Old 22nd May 2013, 10:56 AM   #14
roline is offline roline  United States
diyAudio Member
 
roline's Avatar
 
Join Date: Sep 2010
Location: East Tennessee
Just an example of a PCB based 6L6 family PP amp.. PCB with electrolytics on the bottom side away from the tube heat works just fine. Top plate is just warm to touch after 4hrs....
For a PPP amp, it may be best from a PCB design stand point to have the output tubes off of the PCB and have the PCB as the driver circuit, bias control and power supply filtering. That would reduce the size, wire it to the output tube sockets similar to the Dynaco designs.
Attached Images
File Type: jpg 6.3 chassis side_c.jpg (111.2 KB, 444 views)
File Type: jpg 8.0 Assembled_b.jpg (156.1 KB, 383 views)
__________________
SO many tubes, SO little time!!!
  Reply With Quote
Old 24th May 2013, 06:41 PM   #15
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Quote:
Originally Posted by funk1980 View Post
Cool! I like tinkering with values too
I totally get the inrush limiter (I've got a very active thread going regarding the best way to do this. Very informative. link). But why would you want to warm up the tubes completely before applying HT?? It will only stress the PSU.
Lookd at the thread and went back to revisit some of the 'Guesses' that I made, and they were all wrong

Did some more work on the power supply designer (duncan amps) and came up with a better shot for the resistor, more like 5-10k depending on the where the relay will be OK switch it out of circuit. The relay is rated 350 volts DC into resistive load, but not sure how that may relate to switching with a capacitive load it it matters. Would like to see the caps charged to 350V or more when it overrides the resistor (nominal 500V supply).

The time constant for the delay is also a bit tricky. If you have it too long (to charge the caps more and reduce voltage across the resistor) you start getting into where the tubes are drawing significant current and that's not good for the relay and resistor. Also depending on the rectifier type silicon (Fast start), 5U4 (Medium start), or GZ34 (slower) the delay may be a problem for tube rectifiers if they come up slow as well as the rest of the tubes start drawing current but not enough time to charge the caps. This is all a guess, but in looking at the PSU Designer you can see a curve where you have a high enough charge and time delay works OK so the resistor doesn't blow due to heat.

That was the last part I looked at (and in the mentioned thread too) that the resistor will have to be a fair sized wattage at 10K, even more at 5K. I Have on the board a spot for a 10-14W wire wound and will add a second set of pads for an additional one in parallel if peak start up current is a problem with heat or resistor reliability. Dissipation with a 10K was in the 25 Watt range peak, 10+ watt resistor _may_ work if in circuit for a few seconds, but the extra resistor would be available if a problem. The 5K resistor may be better but again, may need to use 2 10+ watt resistor to support the inrush current and heat.

Will just have to give them a try and see how it works heat wise and the life of the relay.

Sandy
__________________
Working on electronics www.EZ260.com and cars www.GTSparkplugs.com
  Reply With Quote
Old 24th May 2013, 08:12 PM   #16
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
25 watt resistors?

That design can be made so much more efficient.
  Reply With Quote
Old 24th May 2013, 08:26 PM   #17
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Quote:
Originally Posted by kingneb View Post
25 watt resistors?

That design can be made so much more efficient.
Peak wattage needed for a 10K resistor would be 25 watts, and I'll bet a 10 watt will be fine. That's a 2 dollar part. If not, toss in a second one for another 2 bucks. Are you worried about cost? It seems like a simple solution to me, and it's 99% out of circuit so nothing to worry about after it's up and running.

25 Watts would be the size needed for a 10k at 500v if a short on the other end of the resistor for total dissipation. The charge of the cap decreased this in a couple of seconds to much lower value then its out of circuit before it's toasted. Am I 100% sure it will work? No, but seems like it would if the peak does not toast the resistor. Am I confidant 2x 10watt resistors would work, yes, net cost 4 bucks, simple design.

Here's the worst case, I remove the relay, jumper the resistor and just turn the amp on.

I think this is just a matter of finding the right resistor value and it's all good, really doesn't seem to me to need to be more complicated then that. As soon as I get a board done, will report on this part of the amp.

Sandy
__________________
Working on electronics www.EZ260.com and cars www.GTSparkplugs.com
  Reply With Quote
Old 24th May 2013, 08:32 PM   #18
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
I always find resistive divider values through trial and error. Start with something that will deliver a ballpark value. A simulation is an OK approximation. You may have to keep a stock of large resistors on hand or use a huge rheostat. I like the rheostat idea. It will be expensive but it is worth it for a piece of test equipment.
  Reply With Quote
Old 27th May 2013, 12:16 AM   #19
SandyG is offline SandyG  United States
diyAudio Member
 
SandyG's Avatar
 
Join Date: Jul 2011
Location: Los Angeles
Prototype of board with parts stuffed.

NOTE : Caps go on the bottom of the board not on top as seen in the pic

Sandy
Attached Images
File Type: jpg EZ125-Proto.jpg (157.3 KB, 351 views)
__________________
Working on electronics www.EZ260.com and cars www.GTSparkplugs.com
  Reply With Quote
Old 2nd June 2013, 11:20 AM   #20
diyAudio Member
 
Join Date: Aug 2008
Hi, SandyG,

Very nice, good looking assembly

I have a couple of notes (from my past experience with Williamson type amplifiers):

1) Cathode followers are not necessary. They serve no purpose but add additional pole. Better to use parallel 6SN7 in push-pull driver of output stage (V5 on your schematic), as it have been done in 400W RCA Williamson amplifier.

2) HF stabilization RC network between anode and grid#2 (100pF + 1K) - is it really necessary? Disconnect NFB, and load your amplifier at full power at 20, 100, 2,000, 10,000, 15,000 and 20,000 Hz, then repeat this procedure with GNFB on.
If there is no oscillation of UL output stage, these networks can be removed. Or you can try to measure leakage inductance of your output transformer. If its below 8mH Williamson most likely won't need it.

3) You can tune up input stage and concertina phase splitter according to article "Improved Williamson Amplifier" for minimum distortions. Google for it, it is available from many sites.

4) If you encounter problem with motorboating, shunt coupling capacitors leading to output stage with 1M resistors, as advised in article "Modernize your Williamson Amplifier" by David Hafler. Raise your BIAS voltage to the maximum level before that !!!

5) NFB fixed resistor should be replaced with trim pot + on/off during testing/debugging.

6) Williamson is quite tricky in terms of stability (which had to be checked at different frequencies and output levels), so it is more convenient to make test build on breadboard. Like the one shown below.
Attached Images
File Type: jpg DSF1169.jpg (291.5 KB, 340 views)
File Type: jpg DSCF0011.jpg (109.3 KB, 316 views)
  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
EZ125 Amp Project SandyG Tubes / Valves 0 30th July 2012 12:43 AM
Quad KT88 driver BRSHiFi Tubes / Valves 6 11th April 2011 05:20 PM
FS: Ei/Yugo KT90 quad, 6H30, svet KT88 quad - melbourne avian Swap Meet 9 15th April 2010 06:46 PM
Quad KT88 oscillation problem chris.busch Tubes / Valves 15 26th January 2009 01:34 AM


New To Site? Need Help?

All times are GMT. The time now is 07:00 PM.


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