[Collins] 572B and the 30L1

[Jim Brannigan]

Early in my Amateur career I built several 811A and 572B amplifiers in 
various configurations.



1)      You can't use 811's in the Heath amplifiers because the plate 
voltage is way over the (1500VDC MAX.) 811 limits.

2)      572B's in the Collins amplifier will not increase power (E x I = P). 
Even if you could increase the Plate Voltage in the 30L1, it would require 
reconfiguring the output tank circuit for the new plate impedance.

3)      The 572B with graphite anode is a rugged tube.  My extended "tests" 
with 811A's would heat the plates to red-hot and warp them in no time. (811's 
and 811A's were surplus and cheap).

4)      In a 30L-1 with no or bad 811A's, I would give serious consideration 
to using 572B's (cost vs. benefit analysis). If the 811A's were good I would 
not replace them.



Jim


> Around and around we go.  For the life of me I can not find any true or 
> sound advantage to replacing the 811's in the 30L-1 with 572B's.
>
> Let me say that Glen is absolutely correct as well as those statements by 
> Jerry regarding the correct tube configuration for the 30L-1.  Be sure the 
> plate orientation is correct or likely failure will occur.
>
> The way I see it, quality 811's suitable for use laying on their side are 
> available for reasonable prices.  The 572B's are also readily available 
> but for somewhat higher prices.  The output of the 30L-1 amp is no greater 
> with 572B's nor is the IM improved when utilizing the 572B's.  As to 
> longevity, the 811's in my amp are 40 years old and have 1000's of hours 
> of usage. Should I replace them with new 811's then I'd expect them to 
> last another 40 years at which time I'll be 105 years old and perhaps a SK 
> long before that. I can't take the amp with me so again, I find no 
> advantage.
>
> Now as to using the 572B's in the SB-200, it was designed to use 572B's. 
> That's a given and a must for that amp.   The 30L-1 was designed to use 
> 811's.   In this case comparison of amps,  "A" does not equal "B" nor does 
> "B" equal "A".  While the plate dissipation of the 572B is greater than 
> the 811 there is nothing to be gained by this fact.  The input power vs. 
> output power of the 30L-1  is the same regardless of which tube is used. 
> Thus the added plate dissipation capability of the 572B factually provides 
> no advantage.   As to 572's running cooler, I don't see this as being 
> correct as plate dissipation result is heat.  My physics book says that 50 
> watts of dissipation  from one tube is equal in heat the 50 watts of 
> dissipation from a different tube.  Roughly, input power minus output 
> power equals dissipation.
>
> The only thing I can find to be gained by using 572B's in the 30L-1 is the 
> basic inflation of ones ego.  Perhaps that's worth the aggravation in 
> changing tube types and the dollars to obtain them.
>
> 73
> Bob, K4TAX