amp question

[Larry Gauthier]

Ray,

Speaking from a Heath perspective, with SB-200s and SB-220s in mind, I can
tell you that the risk is not that you are pushing the tubes too hard (idle
current) - because there was enough head-room in the designs that the tubes
are not at risk of melting down as you operate. However, the REAL issue is
decreased tube life - particularly of the 3-500Zs in the SB-220. As you may
know, the designer engineers at Heath intentionally chose a filament
transformer that would under-supply the tubes, rather than the over-supply
practices of some_other_ vendors (one that starts with a "D" comes to mind)
at the time who could demonstrate that they could eek-out a few extra watts
from their 3-550 amps - at the cost of tube life.

With the gradual upward climb of primary household voltage from 115 to now
around 130, the under-voltage filament design has evaporated.

-larry
K8UT
a former ham from heath

----- Original Message -----
From: "rayfri" <rayfri at NETWORLD.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Thursday, January 03, 2002 3:27 PM
Subject: amp question


> I've seen several advisories pertaining to amps such as the 30L-1 and
> possibly the sb-200 to the effect that because of higher liner voltages
> today
> (when the amps were designed, line voltage was around115 volts) the
> idling current could be too high for the 811's and 572b tubes.  Several
> mods
> have been offered to lower the idling current.
> Is this information something that should be taken seriously and the
> mods
> used, or regarded only as a possible mod, such as the Harbach mods......
>
> nice, but not essential?
> Ray  WA7ITZ
>
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