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 Post subject: Gonset GSB-100
PostPosted: May Sat 15, 2021 1:46 am 
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Joined: May Sat 15, 2021 1:36 am
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I have to replace the Choke2 in the low voltage supply, among other problems. This choke is connected to two vertically mounted resistors on top of the chassis, which are not shown in my manual's schematic. These identical resistors are 10 ohms each. To avoid any mistakes in repair, can anyone tell me how these resistors are conected to Choke2?

Thanks, Al, N6ZI


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 Post subject: Re: Gonset GSB-100
PostPosted: May Sat 15, 2021 3:05 am 
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Joined: May Thu 17, 2018 12:16 am
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Location: Edmonds, WA USA
You need to visually determine how they ae connected from the choke input and output so we can help. Do they go to chassis ground? Across the choke? Whatever? You are correct that they are not on the schematic. Has the choke been replaced previously or is it original.

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 Post subject: Re: Gonset GSB-100
PostPosted: May Sat 15, 2021 3:07 am 
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Location: Edmonds, WA USA
PS What is the ohms value of the resistors and the likely wattage? A picture would help.

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 Post subject: Re: Gonset GSB-100
PostPosted: May Sat 15, 2021 3:52 am 
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Hi Al, and welcome aboard.

I see one "tapped" resistor topside, R-25 a 25K WW, and its the bleeder for the HV not the low B+. Its located next to the choke and small can elect cap, as in the pic below. I don't see any bleeder for the Low B+, anywhere off/after CH2, nor any ten ohm resistors.

Image

Image

Image

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 Post subject: Re: Gonset GSB-100
PostPosted: May Mon 17, 2021 9:26 pm 
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Joined: May Sat 15, 2021 1:36 am
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W7vm

Thanks for all your pix and info. Instead of the single bleeder attached to the HV, I have two bleeders attached to the LV supply.
Crazy no. The rig was working fine, but now Choke2 is open. I have ordered a replacement Harrison choke. 73, Al, N6zi.


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 Post subject: Re: Gonset GSB-100
PostPosted: May Mon 17, 2021 10:11 pm 
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If the HV is bleeder is missing, your rig has been seriously monkeyed with by a prior owner. The HV bleeder serves not only to keep a sufficient load on the HV supply when the final is in standby but also to act as an equalizing resistor for the two series connected HV filter capacitors. It is NOT an optional item, maybe it has been moved but if it has actually been removed from the circuit it needs to be replaced.

The LV supply shouldn't have those 10 ohm resistors in place and 10 ohm resistors definitely aren't bleeder resistors.

I would carefully put this rig back to stock. It is a well designed transmitter and one of the best of the phasing type with its crystal notch filter that makes carrier balance less critical than other phasing rigs.

The only weak spot is transformer failure so you definitely don't want the power supply to be monkeyed with by some clueless ham who thought he knew more than the designers.

Figure out what is missing and put it back as Gonset intended.

Rodger WQ9E


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 Post subject: Re: Gonset GSB-100
PostPosted: May Mon 17, 2021 10:27 pm 
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Joined: Mar Thu 04, 2010 3:09 am
Posts: 92
I also have a GSB100 with an issue, though a different one. It recently stopped working and the small xformer seen in the lower left (near the relay) labelled 273004 of the overhead pic started cooking. I immediately powered down. Does anyone know what that transformer is for. I have most of the manual for it but it is not identified in what I have.

Since it starts to cook as soon as I power it on I cannot check the circuit and tube voltages. A few years ago I completely recapped it but a bad cap is still possible.

This is a nice xmitter and I'd like to set it back up for AM.

Thanks, Rich


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 Post subject: Re: Gonset GSB-100
PostPosted: May Tue 18, 2021 3:49 am 
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Location: Liberty, Missouri
That's the audio driver transformer T-1. Pull V2 and V3, it most definitely should not smoke. Re-install the tubes one at a time to see which causes the problem.

Image

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 Post subject: Re: Gonset GSB-100
PostPosted: May Tue 18, 2021 4:24 am 
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Joined: Mar Thu 04, 2010 3:09 am
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Great advice. I suspected it was in the audio chain but did not know for sure. Pulling the tubes will be an easy check.

Thanks, Rich
WD4DMZ


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 Post subject: Re: Gonset GSB-100
PostPosted: May Tue 18, 2021 8:17 pm 
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This morning I pulled the tubes and turned on the transmitter. Unfortunately the transformer started cooking immediately. Removed V1, the 12AX7 as well and it still sizzled. The tubes all test good with high emission, no grid leak or shorts. Most likely there is a component failure inside one of boxes in the chain... the low pass audio filter or the phase shifter into V3.

I found the schematic and it identifies the filter and shifter but does not identify the ratings of the components inside. I recently recreated a couplet for an old Globe Scout but the internals were easily identified as they were generic components. The ones in this Gonset are probably specific to the transmitter. Anyone have any idea what is inside these filters?

Most likely I will set this aside for a later date as I do not see and easy fix.

Rich


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 Post subject: Re: Gonset GSB-100
PostPosted: May Wed 19, 2021 3:25 am 
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Location: Edmonds, WA USA
I suspect that T1 has a short between the primary and core therefore to ground. Disconnect the low pass network from the transformer and put a current meter in series with the B+ feed and watch the meter. If there is current draw the primary is shorted. To clarify, the B+ rail should feed only one end of the transformer primary and nothing connected to the other end of the primary winding. If shorted this might be good news as T1 should be easy to replace with a modern one. The low pass filter is just ordinary parts. The unobtanium part is the phase shift network as the component values were probably hand selected by a specialty manufacture.

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 Post subject: Re: Gonset GSB-100
PostPosted: May Wed 19, 2021 3:18 pm 
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Joined: Mar Thu 04, 2010 3:09 am
Posts: 92
Good guidance and worth a try. I see that B+ feed on the schematic.

Thanks, Rich


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 Post subject: Re: Gonset GSB-100
PostPosted: May Thu 20, 2021 10:24 pm 
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Joined: May Sat 15, 2021 1:36 am
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My apologies. The two wirewound resistors are 10kohm each and are connected to the HV supply. I have received a Hammond choke from Digikey and am in the process of replacing choke2 with it. Thanks for all your helpful replies.

Al, N6zi


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 Post subject: Re: Gonset GSB-100
PostPosted: May Fri 21, 2021 12:15 am 
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Location: Liberty, Missouri
Be sure to check the filter caps, C15A and B, 40 uF 450 Volts, and the B+ line to verify there is no short or low resistance on the output side of the choke.

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