Power Transformers. Decisions - 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 21st March 2006, 12:33 AM   #1
kff322 is offline kff322  United States
diyAudio Member
 
kff322's Avatar
 
Join Date: Mar 2006
Location: Berkeley Heights, NJ
Send a message via AIM to kff322
Default Power Transformers. Decisions

Hello World,

Does anyone know the specs or a power transformer that would be a good match in a Harman Kardon Citation II?

Thanks Guys
  Reply With Quote
Old 21st March 2006, 12:43 AM   #2
diyAudio Member
 
Join Date: May 2005
Location: California
My SAMS fotofact says:
180v @ 1.7 amps,
6.3v @ 6 amps,
70v @ 10ma (?) for bias,
and
6.3v @ 6 amps
  Reply With Quote
Old 21st March 2006, 12:51 AM   #3
kff322 is offline kff322  United States
diyAudio Member
 
kff322's Avatar
 
Join Date: Mar 2006
Location: Berkeley Heights, NJ
Send a message via AIM to kff322
Thanks a lot
Now does anyone know of a suitable replacement?
hmmm
  Reply With Quote
Old 22nd March 2006, 05:04 PM   #4
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I used to sell these on eBay, you might try there from time to time..
Otherwise you are probably talking about a custom made replacement.

Are you repairing an existing Citation II or building one from scratch?

I used to repair and restore lots of these in the 1990's as part of my day to day business, and am quite familiar with the design and its limitations. (Yes it's not perfect )

If you are building one from scratch check out my site and find the old OTS/PF articles there as there are a number of mods mentioned in them that you might find useful.

If scratch building I do not recommend using the stock doubler circuit, this will give you a range of choices from Hammond.
Note that the idle current in the Citation II was 100mA per tube, and this is a huge burdon on any extant power transformer, not to mention the fact that the only modern tube I have seen that can handle the dissipation at 450V is a KT99.. Otherwise I would run them around 60 - 70mA.

You could use 750VCT - 800VCT @ 500mA transformer to run a clone Citation II. Or as mono blocks 750VCT - 800VCT@ 250mA should work fine, in both cases assuming tube rectification.. Something in the Hammond 37X series ought to work. Using solid state fullwave (not bridge) rectification something right around 700VCT@ >500mA would be ok. If you elect to use a bridge 360V @ >500mA would be fine for a stereo amplifier.

One of my more popular mods was to boost the B+ to about 540Vdc, this made a surprising difference to the sound quality. I also had an entire line of amplifier designs (and a few commercial amplifiers) built around Citation II iron. MFA built a line of 120W monoblocks using a single Citation II output transformer, and I also built some commercially. This output transformer is very conservatively rated for a 60W transformer, and in fact with 540V B+ and a quartet will easily get over 100W..

Hope some of this is helpful and not too far off topic.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 23rd March 2006, 01:56 PM   #5
kff322 is offline kff322  United States
diyAudio Member
 
kff322's Avatar
 
Join Date: Mar 2006
Location: Berkeley Heights, NJ
Send a message via AIM to kff322
I am building a clone,
Because large power transformers are very expensive, I am planning to build a 4 stage voltage doubler, bring 120 Volts to around 480 Volts.Would there be any problems in doing this?

Btw - Your site was very useful!
  Reply With Quote
Old 23rd March 2006, 02:19 PM   #6
Tweeker is offline Tweeker  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Cincinnati, Ohio
Your not trying to omit the transformer I hope? Dont.

Look to industrial transformers for cheap power iron. If bridge rectification is ok it might be tenable use a 120V winding in series with a 240V winding or 2 120V windings for 360VAC.
__________________
Be sure your foil hat has a good low impedance ground.
  Reply With Quote
Old 23rd March 2006, 03:39 PM   #7
kff322 is offline kff322  United States
diyAudio Member
 
kff322's Avatar
 
Join Date: Mar 2006
Location: Berkeley Heights, NJ
Send a message via AIM to kff322
I am still using an isolation transformer of course! But whats wrong with a voltage doubler?
  Reply With Quote
Old 23rd March 2006, 04:10 PM   #8
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
They have very high output impedance. Also, your isolation transformer may not be up to the job of isolating those voltages. Go for kevinkr's suggestion and use a proper transformer, 360V with a bridge would do nicely. Money saved on transformers is time wasted on construction. You're building it to produce something good so don't skimp on the materials.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 23rd March 2006, 09:24 PM   #9
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
I agree, voltage doublers are OK for low current. I use one myself, for the negative supply in my amp, to feed voltage amp stages and to bias the OP tubes. The current involved is less than 30mA and it's all class A (doesn't vary with the signal).

However, for the main B+, which has to supply all stages, including the OP tubes whose current demand depends on the signal amplitude (unless they're in class A), you need a low impedance supply. A voltage doubler is not a very good solution for this. (I know that H-K used one but I think it must have been for economy reasons).
  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
Help identifying a pair of output transformers and power transformers mjk130 Parts 3 30th January 2009 10:44 AM
Midrange -decistions -decisions... mp006ltk Multi-Way 21 6th November 2007 08:41 AM
Decisions... P101 vs. P3A vs. SKA RyanW Solid State 34 3rd November 2006 08:33 PM
sub decisions v1d9uy Subwoofers 3 30th July 2006 02:54 PM
Decisions, Decisions - Help me select iron kstylianos Tubes / Valves 7 14th February 2006 12:05 AM


New To Site? Need Help?

All times are GMT. The time now is 11:49 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