Gonset Gsb 101 Manualidades
I have obtained an excellent condition old Gonset GSB 101 amplifier. This amp originally used four 811A tubes, and used a full-wave HV supply with a pair of 866 rectifiers. This gear was originally used with separate transmitters and receivers, and while there is internal operating bias of about -4 volts DC, full cutoff during receive was to be provided externally,-100 vdc was suggested for that function. SO, here's the deal - I have converted the HV supply to solid state, removed the OEM negative lead filter choke, and plan to increase the OEM HV bleeder from 50K ohm, to 100K ohms - primarily as providing less HV bleed-down, while decreasing power transformer drain and heat - at some point, might remove bleeder completely and let the string of new electrolytic 100K equalizing resistors handle the bleeder function. Download encyclopedia of spirits pdf download.
At this point, I have installed a full set of 572B finals - NOT to run this amp with additional power, but they are what I had, and have lots better plate dissipation than the old 811A's. SO, my question is, is using the power transformer center tap to switch HV from transmit to receive recommended with an old center-tapped power transformer rather than installing an internal source of switchable bias for transmit/receive? I would expect a pretty heavy instantaneous current surge using the center tap, since the new filter caps I installed have about 300% more filtering capacity than the OEM, and due to age of this amp, really would hate to blow the power transformer if typical 'old-time' center tap HV switching is too heavy an added load going from transmit/receive. YUP - plenty of room - and I have the stuff needed to make up a -100 vdc bias supply - but the center tap switching just seems simple and 'alluring' - used to do that all the time 'back in the day' - but the later shift from full wave transformers/rectifiers to voltage doubling and such, has done away with center tap as a source for HV switching. All I'd have to do to switch the center tap, is add a single relay, rather than a complete relay AND the -100 vdc circuit. The GSB 101 already handles the RF internal switching with a transceiver with no mods. Thanks for the reply.
Gonset Gsb 101 Manualidades 1
YUP - plenty of room - and I have the stuff needed to make up a -100 vdc bias supply - but the center tap switching just seems simple and 'alluring' - used to do that all the time 'back in the day' - but the later shift from full wave transformers/rectifiers to voltage doubling and such, has done away with center tap as a source for HV switching. All I'd have to do to switch the center tap, is add a single relay, rather than a complete relay AND the -100 vdc circuit. The GSB 101 already handles the RF internal switching with a transceiver with no mods. Thanks for the reply.
Click to expand.I forgot it had a relay, but I think it's a high voltage relay normally driven by 120Vac at a terminal strip or something (hazy memory, haven't seen one in probably ten years).I usually get rid of that and use a 3PDT low-voltage, low-current modern relay and add an RCA phono jack so a pull to ground keys the internal 12Vdc 100mA relay; two sets of contact used for RF and one set used for bias keying. The relay from the common modern-day Ameritron amps, which costs about $10 or something, works fine for this. YUP - plenty of room - and I have the stuff needed to make up a -100 vdc bias supply - but the center tap switching just seems simple and 'alluring' - used to do that all the time 'back in the day' - but the later shift from full wave transformers/rectifiers to voltage doubling and such, has done away with center tap as a source for HV switching. All I'd have to do to switch the center tap, is add a single relay, rather than a complete relay AND the -100 vdc circuit.
The GSB 101 already handles the RF internal switching with a transceiver with no mods. Thanks for the reply. Click to expand.I would not switch the center tap, for four reasons:1) Some plate transformers weren't designed to be operated with the center tap ungrounded, or close to ground potential. I don't know about the GSB-101, but would you want to find out the hard way?2) You have removed the filter choke, solid-stated the rectifiers and upgraded the filter caps for the higher voltage.
If you disconnect the supply every time you go to receive, there will be the enormous charging current every time you go to transmit.not good. The Ancient Ones did this because they used choke-input filters, which limit the charging current on start-up.
Eliminating the choke eliminates its current limiting.3) If you want to use the relay anyway, why not do it on the primary side of the plate transformer?4) Note that the center-tap of the 811A filament transformer is grounded. This connection could be opened and a suitable resistor or Zener inserted, and shorted by a single relay contact in transmit. This method won't achieve full cutoff of plate current, but it can be greatly reduced.73 de Jim, N2EY.