Go Back   Home > Forums > > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubelab Discussion and support of Tubelab products, prototypes and experiments

Reply
 
Thread Tools Search this Thread
Old 24th September 2017, 08:01 PM   #1
colnago55 is offline colnago55  United States
diyAudio Member
 
Join Date: Feb 2016
Location: New York City
Default 300B TSE B+ mystery

Hi,

When I bench tested my new 300B build, I had a B+ of 418 volts. Now that I have it built and in its chassis, the B+ has dropped to around 360 volts. The only change that I can think of is that I added a CL-90 to the power input.

I am using the 660 volt leads from an Edcor xpwr 131. I'm using a Triad c-14x choke.

C4 is a 47 uf 500 volt cap

c5 is a 150uf 500 volt cap in parallel with 100uf motor run cap

The amp sounds fabulous, except that I hear a strange crackle for a second as it powers up. No hum, lots of punch. Sounds more engaging than my TSE 45.

I'm using JJ 300B tubes which are huge.


Could the CL-90 be causing the drop in B+ and also the noise. Should I be using a different current limiter?

I'm happy to live the 360 B+, just don't understand why the change.

thanks, Jacques
  Reply With Quote
Old 26th September 2017, 11:14 AM   #2
zxx222 is offline zxx222  Europe
diyAudio Member
 
Join Date: Aug 2005
Location: b
cl-90 should not drop voltage. check bias of 300b's - higher bias current is most probable reason for lower B+.
  Reply With Quote
Old 26th September 2017, 11:51 AM   #3
colnago55 is offline colnago55  United States
diyAudio Member
 
Join Date: Feb 2016
Location: New York City
That could be it. I am using panel meters now while on the bench test I used multimeters.

Is there a way to check the accuracy of the panel meters? would measuring across them give an accurate reading?
  Reply With Quote
Old 26th September 2017, 12:29 PM   #4
zxx222 is offline zxx222  Europe
diyAudio Member
 
Join Date: Aug 2005
Location: b
Voltmeters or ammeters? Ammeters are supposed to be wired instead 10R resistors, not across them.

In any case you can make simple circuit with battery and resistor corresponding to your tube bias current and compare what your panel meters show in comparison to multimeters.

Chinese panel meters are not precise and I remember I had to adjust mine for 80mA current using above mentioned circuit and multi meter as reference.
  Reply With Quote
Old 26th September 2017, 12:39 PM   #5
colnago55 is offline colnago55  United States
diyAudio Member
 
Join Date: Feb 2016
Location: New York City
Yes, I am using Chinese ammeters in place of the resistors.

I'll try your suggestion to calibrate them. Any suggestion on the battery and resistor to be used?



Thank you. Jacques
  Reply With Quote
Old 26th September 2017, 01:48 PM   #6
zxx222 is offline zxx222  Europe
diyAudio Member
 
Join Date: Aug 2005
Location: b
Ohms law depending on what battery you have and your bias. I used 1,5V battery and 0,5w 30ohms trimpot to set resistance exactly to 18,75R for 80mA current across it, then connected panel meters (not simultaneously) inline and set them to be spot on for 80mA.
  Reply With Quote
Old 26th September 2017, 04:15 PM   #7
w5jag is offline w5jag  United States
diyAudio Member
 
Join Date: Feb 2007
Location: Arkansas
What rectifier tube are you using?

With a 5AR4, 330-0-330, CLC config, I would expect about 410 - 420 volts dc loaded, which is what you report you had on the bench.

Check the bias by all means, but I am doubtful that it could be so far out of adjustment as to drop 60 volts, without the tubes glowing red hot.

Is it possible you have made a measurement mistake, e.g. DMM set for AC when you are trying to measure DC?

You might want to check the voltage at the + lead of each capacitor and then at the bleeder resistor - maybe something is leaking to ground. If you have an aux cap, disconnect it and see if that makes any difference.

Win W5JAG

edit: the crackle sound on startup is not normal, and is a symptom of something ..... Long shot - a bad solder joint on one of the capacitors in the B+ or B- chain. You might be hearing some arcing as the voltage tries to get between the two layers of the board. Do you also smell a whiff of ozone? If so, you have lightning somewhere ....

Last edited by w5jag; 26th September 2017 at 04:20 PM.
  Reply With Quote
Old 26th September 2017, 04:26 PM   #8
colnago55 is offline colnago55  United States
diyAudio Member
 
Join Date: Feb 2016
Location: New York City
Yes, I'm using a 5AR4. I checked the measurement with two different meters.

I have the panel meters in place of the bleeder resistors. I will check the aux cap.

thanks, Jacques
  Reply With Quote
Old 28th September 2017, 06:09 AM   #9
zxx222 is offline zxx222  Europe
diyAudio Member
 
Join Date: Aug 2005
Location: b
Quote:
Originally Posted by w5jag View Post
What rectifier tube are you using?

With a 5AR4, 330-0-330, CLC config, I would expect about 410 - 420 volts dc loaded, which is what you report you had on the bench.

..
Are you sure about that? I made quick sim in PSUD, with 330-0-330V and 184mA total current for all tubes, B+ is 370V. If 300B's are biased to 100 mA each, then B+ drops to 360V.
  Reply With Quote
Old 28th September 2017, 02:47 PM   #10
w5jag is offline w5jag  United States
diyAudio Member
 
Join Date: Feb 2007
Location: Arkansas
Quote:
Originally Posted by zxx222 View Post
Are you sure about that? I made quick sim in PSUD, with 330-0-330V and 184mA total current for all tubes, B+ is 370V. If 300B's are biased to 100 mA each, then B+ drops to 360V.
A generic PSUD sim will show a lower voltage, but we don't have enough information to model it - we don't know the actual line voltage, or exact parameters of his specific components. Adjust the line voltage up 4%, and see what you get .....

The real world rule of thumb I have always used, and ( for me ) seems to hold up well for the typical 117VAC PT, being used at contemporary U.S. line voltages, is that with a 5AR4 rectifier, CLC configuration, loaded B+ will be about (1.25)(VAC).

(330)(1.25) = 412.5, so I would expect loaded B+ to be somewhere within 10 or 15 volts of that, either way, assuming the first C is not an unusually small value.

I don't know how you model or sim a start up crackle.

Win W5AJG
  Reply With Quote

Reply


300B TSE B+ mysteryHide 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
New 300B - TJ Full Music 300B CNE DIY Hifi Supply DIY HiFi Supply 15 22nd June 2017 05:39 PM
FS: for 300B (JE Labs 300B SE) builders cartman Swap Meet 2 29th October 2008 01:13 PM
little 6.5 mystery ... oface Full Range 6 4th November 2007 11:20 PM
* 35 watt * 300B SE = super 300B + Class A2 rick57 Tubes / Valves 4 13th July 2005 04:18 PM
mystery... mista2 Multi-Way 1 14th January 2005 04:20 AM


New To Site? Need Help?

All times are GMT. The time now is 10:37 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki