DC filaments for 6550s - 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 4th September 2009, 05:53 PM   #11
diyAudio Member
 
Join Date: Jul 2003
Location: Ann Arbor, MI
hey-Hey!!!,
There are published limits on grid circuit resistance. This is because there is a bit of grid current, and it must not be able to disrupt the grid voltage( through the resistance ) in any significant way. The 6550 is a high gm tube, and IIRC it was spec'd for maximum grid circuit resistance of 250k in cathode bias. You'd be at 2x that with the 510k...waaaaaay to high IME. Besides, the power tubes wind up sounding better with less resistance there anyway.
cheers,
Douglas
__________________
the Tnuctipun will return
  Reply With Quote
Old 4th September 2009, 10:49 PM   #12
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by puginfo405 View Post
Hi Salas, thks for the input. im not clear what is the difference between the 510k and 220k grid resistors. is this a safety issue here ("run away out") that they need to be changed? BTW im on 6550 (not the KT88 as in diagram).

OK the OPT is the Hammond 1650R, 5k p=p, 318ma max.
PT is 500mA, 420Vac secondary and the rest ie 6.6vacX2, 5A and 15Vac etc


cheers
Yes its not safe. Explanation covered by the other members.

Your Hammond is a ''slow'' one, can't use the same compensation cap as from original, especially if you get your grid leaks down to 220k. I agree with kevin, its better to modify. 12AX7's can't push treble if you go down on the grid resistors. Well, they cant push 6550's anyway. Have a look at a reasonable way of handling those tubes for driving KT88/6550. The example is the GEC 50W classic.
Attached Images
File Type: gif gec50w.gif (29.9 KB, 193 views)
  Reply With Quote
Old 5th September 2009, 02:10 AM   #13
diyAudio Member
 
Join Date: Jul 2003
Location: Ann Arbor, MI
-----Your Hammond is a ''slow'' one...

That particular Hammond is a *FINE* opt. I've found that one far better than expected, even compared to some very fine units.
cheers,
Douglas
__________________
the Tnuctipun will return
  Reply With Quote
Old 5th September 2009, 01:11 PM   #14
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Is the published 30kHz bandwidth a typo?

EDIT. Searched about a bit, and I have seen that an analogous Lundahl 1679 (105W 4.5K P-P UL taps) is quoted 70kHz, that is a double C core. Also a Hashimoto HW-100-5 (Double C type?) shows a chart with -3dB at 80kHz without a primary impedance resonance somewhere, though it is an expensive unit. Those are claims of course and I don't know what happens when they get stressed.
Its nice to know that the 1650R can do fine, because good OPTs tend to cost an arm and a leg these days. Surely we can not expect any compensation scheme found in an original schematic that worked with some certain and sometimes dedicated transformer to work for any other. Our friend needs an oscope, a gen, and some 10kHz squares to tune whatever assortment he ends up with.
  Reply With Quote
Old 5th September 2009, 04:25 PM   #15
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by puginfo405 View Post
Im looking into getting the 6550s to run with DC to get hold off some hum issue. i have dual 6.6V ac windings at 5 amps now at the PT. has anyone a simple and reliable cct to do this? im thinking of a std 3810 bridge diode pack for this and a cap of say 10,000uF and some dropper resistors to keep it simple.
Before you spend the time and $$ to build a DC supply try powering the heaters with a battery. A few D cells will do it. If that kills the hum then go for it but if you still have hum with the battery supply then the heaters are not yor problem.

Recently I had a hum problem that did turn out to be the hearer supply. I was letting the voltage float. I made a "artificial center tap" using two 100R resisters to ground and the preamp was them silent.

OK if you do build a big DC supply place the dropper resisters _between_ a two large caps where they can do some double duty as both dropping and filtering. Use a two or even three stage filter.
  Reply With Quote
Old 5th September 2009, 06:04 PM   #16
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
My hunch is, there is a ground loop. AC heating gives absolutely no hum in my 95dB speakers driven by my 31dB gain KT88 20W trioded amp. Dead silent background for hiss also. Its very cramped inside, sporting a 250VA toroid underneath, smack centre. If it can be done like this (took some careful experimentation), it surely can be done easily when space is normal and PTX can be located logically away from signal wiring and sensitive gnd nodes, above a metal top plate. Had to do it in a small chassis as I used a donor one from a Serbian amp that I disassembled but kept the Audio Note OPTs. I had no space for DC heating regulators even for the 12AY7s and 12AT7s. Here is the way I heat it up. It may be of help.
Attached Images
File Type: jpg ACheaters.jpg (52.5 KB, 175 views)
File Type: jpg SalasKT88side.jpg (221.6 KB, 163 views)
  Reply With Quote
Old 6th September 2009, 05:33 AM   #17
diyAudio Member
 
Join Date: Aug 2009
hi all, thks very much for all the valuable inputs in improving this (esp. Kevin and Salas). here i have is the wooden testbed im using now. the input stage 12AU7 is being sheilded by a cake alu can. you can also see the 2 star points for the 12AU/AX and another for the 6550 only. there is also a DC heater module for the AU/AX.

as i read the inputs, it makes sense to move towards Sala's GEC50W cct. so since its a PCB based to start with, im trying to figure the best way to cut up the tracks and reconfig to accommodate the AX->AU->6550->1650R40UL rather than the current AU->AX->6550->1650R40UL.

cheers
Attached Images
File Type: jpg DSC00213.JPG (83.3 KB, 148 views)
File Type: jpg DSC00214.JPG (98.2 KB, 117 views)
File Type: jpg DSC00215.JPG (82.5 KB, 62 views)
  Reply With Quote
Old 6th September 2009, 05:40 AM   #18
diyAudio Member
 
Join Date: Aug 2009
here is the mock up of the actual build. its a dual deck metal frame. lower deck has PT, DC heater reg and HT modules for 6550/AU-AX. upper deck has hammond 1650R and PCB. the whole thing measures up 7in width, 15in length and height about 10in or so depending on the 6550 ceiling. its quite a compact build.

cheers
  Reply With Quote
Old 6th September 2009, 11:44 AM   #19
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Hey! You wonder why you have hum! The pics say the whole story.

Don't even bother to fix it in this style. Seriously.

You are making a Jadis 30 clone. My neighbor has a DA-30. Look at the photos from when I got it here to listen to it and put a couple of Black Gates in. See how it is made?

Punch a nice roomy metal box for power octals and driver novals, set your output transformers atop, set your power transformer with reverse orientation amongst them. Read about star and buss bar grounding, test some suitable for classic 3 stage noval + octal schematics point to point. Look to the many photos here in the DIY tube gallery. See how people are wiring them up and grounding them.
Attached Images
File Type: jpg DA30inside.JPG (358.9 KB, 80 views)
File Type: jpg DA30vsSalas.JPG (222.4 KB, 74 views)
  Reply With Quote
Old 6th September 2009, 02:44 PM   #20
diyAudio Member
 
Join Date: Aug 2009
Quote:
Originally Posted by puginfo405 View Post
here is the mock up of the actual build. its a dual deck metal frame. lower deck has PT, DC heater reg and HT modules for 6550/AU-AX. upper deck has hammond 1650R and PCB. the whole thing measures up 7in width, 15in length and height about 10in or so depending on the 6550 ceiling. its quite a compact build.

cheers

pardon me,the pictures did not upload the first time, so here it is.
Attached Images
File Type: jpg DSC00211.JPG (89.1 KB, 77 views)
File Type: jpg DSC00212.JPG (89.8 KB, 69 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
Tung-Sol (new production) 6550s alexmoose Tubes / Valves 6 30th November 2006 09:48 PM
should the filaments be already hot before the B+ is applied or jarthel Tubes / Valves 15 17th August 2006 01:47 PM
Filaments for the Aikido Kashmire Tubes / Valves 1 2nd August 2005 01:24 PM
6550s Thatch_Ear Swap Meet 0 24th December 2001 05:36 AM


New To Site? Need Help?

All times are GMT. The time now is 09:38 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