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: 811A tube to replace 572B?  (Read 3149 times)
VE1PEW
Member

Posts: 4




Ignore
« on: May 06, 2012, 06:31:32 PM »

I have seen on the Svetlana Datasheet that the 572B tube can be used as a direct replacement for a 811A.  Is the opposite also true.  The datasheet I looked at for the 811A seems to have slightly lower voltage ratings than those on the 572B.  I know where I can get several of these tubes NOS for a great price and was wondering if I should pick up a couple of sets to replace the 572B's in my SB200 if the need arises.

73,Paul
VE1PEW
Logged

Insanity is hereditary.....you get it from your children.

VE1PEW - Licensed amateur since February 2011...a work in progress
KA5N
Member

Posts: 4380




Ignore
« Reply #1 on: May 06, 2012, 06:46:36 PM »

The 572B has a higher voltage rating and a much higher power disapation rating than an
811A.  So you can't use 811A's in place of 572B's.  If you try you will quickly wreck the 811A's
and probably damage your amplifier.

Allen
Logged
K2DC
Member

Posts: 1340


WWW

Ignore
« Reply #2 on: May 07, 2012, 02:58:30 AM »

KA5N's got it right.  Do not replace a 572B with an 811A.  If it doesn't blow immediately, it will very shortly and possibly take out more with it.

73,

Don, K2DC
Logged
G3RZP
Member

Posts: 4326




Ignore
« Reply #3 on: May 07, 2012, 04:36:08 AM »

The 811A has about 1/3 of the plate dissipation of the 572B.
Logged
W8JX
Member

Posts: 5350




Ignore
« Reply #4 on: May 07, 2012, 04:46:18 AM »

Very bad move. They will fail quickly  (if not when you first turn it on) and likely damage HV power supply too if tube arcs over and shorts out. Run properly 572's in a SB200 have a very long life. I would not worry much about needind several spares either. 
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
N2EY
Member

Posts: 3833




Ignore
« Reply #5 on: May 07, 2012, 05:41:10 AM »

The datasheet I looked at for the 811A seems to have slightly lower voltage ratings than those on the 572B.  I know where I can get several of these tubes NOS for a great price and was wondering if I should pick up a couple of sets to replace the 572B's in my SB200 if the need arises.

Short answer: NO.

The voltage rating difference (1500 for the 811, 2000+ for the 572B) may seem slight, but it's not.

Worse, the plate dissipation is very different. The 811A is rated 65 watts ICAS plate dissipation; the 572B is rated 160 watts - more than double!

The 572B/T160L can be used as a direct replacement for the 811A in most applications, but electrically it's at least double the 811A.

The only way to use 811As in an SB-200 would be to modify it for lower plate voltage and current, to get within the much-lower ratings.

73 de Jim, N2EY

 
Logged
W8JX
Member

Posts: 5350




Ignore
« Reply #6 on: May 07, 2012, 06:12:36 AM »


The only way to use 811As in an SB-200 would be to modify it for lower plate voltage and current, to get within the much-lower ratings.
 

Yes if you reduce plate voltage to about 1700 max at idle and limit total plate current to less than 300 ma is would work and you would have about a 300 watt amp too.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
N2EY
Member

Posts: 3833




Ignore
« Reply #7 on: May 07, 2012, 07:08:16 AM »


The only way to use 811As in an SB-200 would be to modify it for lower plate voltage and current, to get within the much-lower ratings.
 

Yes if you reduce plate voltage to about 1700 max at idle and limit total plate current to less than 300 ma is would work and you would have about a 300 watt amp too.

Agreed! At which point it's almost not worth the trouble.

IIRC, amps purpose-built to use 811As would run them at 1500 V / 160 mA or so (under load, each tube). Works out to maybe 500 watts input per pair, 300 watts out on a good day. Such amps were popular with hams running rigs in the 40-50 watt class, which were common in the early days of SSB (single 6146 in the output)

Before the SB-200, Heath made the HA-10 "Warrior" amp. It used four 811As in grounded-grid, with two 866As in the power supply. Cost $229.95 as a kit, $330 wired, weighed 100 pounds, and was much bigger than an SB-200. Ran 1000 watts DC input CW/SSB. (The SB-200 can run a little more on SSB)

73 de Jim, N2EY

Logged
KA5N
Member

Posts: 4380




Ignore
« Reply #8 on: May 07, 2012, 07:44:57 AM »

Now that just about everybody has had their say.  The best thing to do with NOS 811A's
if you can get them cheap, is to buy them and resell on eBay.  You should be able to double
or triple your money. (Assuming of course that they are good tubes).

Allen
Logged
W8JX
Member

Posts: 5350




Ignore
« Reply #9 on: May 07, 2012, 02:50:06 PM »

Now that just about everybody has had their say.  The best thing to do with NOS 811A's
if you can get them cheap, is to buy them and resell on eBay.  You should be able to double
or triple your money. (Assuming of course that they are good tubes).

Allen

Or better yet,  pass it by...
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
N0SQ
Member

Posts: 53




Ignore
« Reply #10 on: May 07, 2012, 03:31:06 PM »

The voltage rating difference (1500 for the 811, 2000+ for the 572B) may seem slight, but it's not.

Are you sure about those voltage ratings for the 811A? I have an AL-811H and according to the manual the HV should be 1700 volts.  According to the manual the voltage can be as high as 1800 volts. Since re-strapping my AL-811H for 240 VAC, the HV is showing as 1.8 kV. So far, no problem.
Logged
W8JX
Member

Posts: 5350




Ignore
« Reply #11 on: May 07, 2012, 04:24:06 PM »

The voltage rating difference (1500 for the 811, 2000+ for the 572B) may seem slight, but it's not.

Are you sure about those voltage ratings for the 811A? I have an AL-811H and according to the manual the HV should be 1700 volts.  According to the manual the voltage can be as high as 1800 volts. Since re-strapping my AL-811H for 240 VAC, the HV is showing as 1.8 kV. So far, no problem.

This is pushing it for a 811. The 572's idle at 2700 volts in my Dentron and have for 18 years now.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
N0SQ
Member

Posts: 53




Ignore
« Reply #12 on: May 07, 2012, 04:58:20 PM »

The voltage rating difference (1500 for the 811, 2000+ for the 572B) may seem slight, but it's not.

Are you sure about those voltage ratings for the 811A? I have an AL-811H and according to the manual the HV should be 1700 volts.  According to the manual the voltage can be as high as 1800 volts. Since re-strapping my AL-811H for 240 VAC, the HV is showing as 1.8 kV. So far, no problem.

This is pushing it for a 811. The 572's idle at 2700 volts in my Dentron and have for 18 years now.

I guess my next set of tubes will be 572's even though they're more expensive.
Logged
VE1PEW
Member

Posts: 4




Ignore
« Reply #13 on: May 07, 2012, 05:36:09 PM »

Thanks for all the replies.  I figured with the lower voltage ratings and plate dissipation it was probably not possible or feasible but it never hurts to check.

73,Paul
VE1PEW
Logged

Insanity is hereditary.....you get it from your children.

VE1PEW - Licensed amateur since February 2011...a work in progress
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!