Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Tubes: 811A vs 572B  (Read 2600 times)
WA2MGB
Member

Posts: 128


WWW

Ignore
« on: January 05, 2004, 05:08:45 PM »


My amp takes four   572B tubes.    I understand that the 811a is a drop in replacement...though more limited in performance.  Given the significant price difference, the 811A  being inexpensive compared to the 572B's... is the loss in performance substantial to warrant spending the extra $ on 572B's?

The amp is a Gonset GSB-201

Tnx
Logged
K0BG
Member

Posts: 9839


WWW

Ignore
« Reply #1 on: January 05, 2004, 05:22:07 PM »

Four 811s have about the same plate capacitance as two 572Bs. Yes you might (!) be able to use them in a pinch, but I wouldn't. The other way around (572s in place of 811s) seldom works. Pay the extra and enjoy the long life driven to the same level as the 811s.

Alan, KØBG
Logged

WB2WIK
Member

Posts: 20542




Ignore
« Reply #2 on: January 05, 2004, 06:03:06 PM »

Ummmm...I've had GSB-201s which came factory equipped with 811A's.  If yours uses 572B's it must be the later version (GSB-201 MK III?) or some previous owner retrofitted it with 572B's even though it didn't need those tubes.

I'd find out which is the case, because 572B's can be operated at much higher plate voltage than 811A's and this is not necessarily a backwards-compatible change.

WB2WIK/6
Logged
AB5Q
Member

Posts: 202




Ignore
« Reply #3 on: January 05, 2004, 08:09:10 PM »

Maximum specified plate voltage for the 811A is 1500 VDC (50% Duty) and for the 572B it is 2750 VDC. Exceeding the tube's maximum voltage rating could result in a plate to grid arc and grid destruction. If your amplifier operates at a plate voltage of less than the maximum allowable for an 811A you should be fine.  It is also important to verify the maximum specified plate current and plate power dissipation for the 811A to make sure you will not exceed those ratings as well.  Tube sockets, plate connectors as well as filament requirements are the same between the 811A and 572B.  Mechanically it is a simple swap, however there are a few electrical variances that complicate things.

Here's a link to the data sheets for both tubes, take a look.

http://www.svetlana.com/docs/tubeframe.html
Logged
KG4PFO
Member

Posts: 174




Ignore
« Reply #4 on: January 06, 2004, 01:28:45 AM »

In short....putting 811's in a amp designed for 572's is NOT a good idea at all......kiss your 811's goodbye.
Putting 572's in a amp designed for 811's on the other hand is acceptable in most cases.
Logged
W8JI
Member

Posts: 9304


WWW

Ignore
« Reply #5 on: January 06, 2004, 09:15:43 PM »

I agree with WIK.

I never saw a GSB 201 that used 572B's from the factory. Every one I saw used 811A's, although 572's were often installed later to be a HD replacement.  

What is the plate voltage? DON'T stick a meter on the anode, read the front  panel meter and tell me.

 
Logged
K8AC
Member

Posts: 1465




Ignore
« Reply #6 on: January 08, 2004, 06:08:24 PM »

I believe the 201 MK III came factory equipped with 572Bs.  MK II was the last with 811As.
Logged
WA2MGB
Member

Posts: 128


WWW

Ignore
« Reply #7 on: January 12, 2004, 02:28:59 PM »


Mine is the Mark IV....factory equipted with 572B's....


Logged
W8JI
Member

Posts: 9304


WWW

Ignore
« Reply #8 on: January 15, 2004, 10:04:29 AM »

Did they raise the HV when they added 572's?Huh

Never saw a MK III I guess!!

Or did they leave the HV about 1700V?
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!