>My old Warrior's parasitic supressors need to be
>changed and I need to know what the optimum value of
>inducatance is for the supressor. The carbon type
>resistors are showing their age as well. Not one is
>even close in value.
>The amp runs four 811A tubes.
// Suppressor resistors (Rsup) typically increase in resistance during
an intermittent parasitic oscillation condition. Thus, it seems likely
that you had one or more. For instance, I have seen Rsup in a MLA-2500
increase from 100-ohms to c. 400-ohms.
- Designing suppressors is not a black art. Lsup needs to have enough L
to cause Rsup to become quite hot on 29MHz. This situation yields
optimal VHF suppression -- i.e., reduction in VHF gain at the VHF anode
resonance of the tube(s). At this frequency, the reactive-ohms of Lsup
and the resistive-ohms of Rsup need to be roughly equal. The only test
equipment needed is a dipmeter. However, my guess is that the Warrior's
anode resonance is c. 80MHz. If this is the case, roughly 0.18uH and
100-ohms would be about right. In a nutshell, more L gives better VHF
suppression with the tradeoff of more heat in Rsup at 29MHz.
- One factor that apparently increased the Warrior's VHF instability was
so-called "neutralization". Heath did not use neutralization in its
subsequent models of GG amplifiers. Gonset also used neutralization in
their 4, 811 amplifier. From personal experience, I know that the Gonset
intermittently oscillated at VHF. The fix was lower VHF-Q suppressors
and removal of the neutralization circuitry.
- For improved transient regultion on SSB, the Warrior's HV supply's
filter choke needs to be resonated at c. 150-Hz. If 572Bs are used, the
filter choke can be shorted out to increase the anode supply voltage and
PEP-out on SSB. However, the increased voltage may necessitate raising
the voltage capability of the filter C.
- For SSB, 811As should be tuned up with a tuning pulser or a keyer
sending 50-wpm dits.
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
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