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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Gonset GSB-201 Help


Reviews Summary for Gonset GSB-201
Gonset GSB-201 Reviews: 1 Average rating: 4.0/5 MSRP: $375.00
Description: Model 3340 Linear Amplifier
Product is not in production.
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KM5VI Rating: 4/5 May 11, 2009 22:56 Send this review to a friend
Vintage Workhorse  Time owned: more than 12 months
This 1960ís vintage amplifier, model 3340 utilizes (4) 811A triodes in parallel, grounded-grid configuration. Some later models, designated MKIII (?) were equipped with (4) 572B finals. The amplifier model 3340 input power is rated at: 1500w SSB, 1000w CW, or 400w AM. Advertised gain is 10db with short duration PEP output of 1000w. Typical peak output power with new tubes in my unit varied from 600w-900w depending on band.

As with most amplifiers of this vintage two modifications are essential for use with modern solid state transceivers Ė a tuned input network and a low voltage keying relay. This amp was not designed with a tuned input circuit so use with modern solid state transceivers requires a tank circuit of some type to be employed between the exciter and the amplifier. You can build one or use a tuner between the amp and the exciter. If you choose the later, try tuning into a 50 ohm dummy load with the amp out of the circuit first each time you switch bands. Tune up the amp next, then tweak the input again to get rid of any remaining reflection. Bear in mind that there will be reactive currents flowing along the outside of the coax between the tuner and the amp so keep the coax length short and arrange sensitive equipment away from this stray RF. The tuner method is OK for testing but adding a permanent input tank is the way to go for permanent use. The original keying relay is 120VAC and externally engaged so some modified keying arrangement must be made. I chose to retain the original relay and use an isolated amp interface.

The amplifier features fixed internal bias with external stand-by cut-off if desired. Approx. -100 volts external bias is required to idle the amplifier during receive. The amp will operate fine without the external cut-off bias, but will dissipate ~250w during idle. This makes for a nice shack heater.

The power supply is 120VAC input only, and not configurable for 240 VAC operation. Peak current draw is stated at 16.7 amps. The bridge is full wave with (4 )silicone diodes per leg. Power supply caps are (4) 100uF in series. As with many vintage amps, expect that the caps will eventually have to be replaced. Mine went south a few years back. High-grade computer type replacements are readily available.

The circuit design uses a condenser plate to couple with stray capacitance given off the tubes for input to the neutralization circuit. The condenser is wired in series with an extra winding on the filament choke in reverse polarity. This simple arrangement circuit works well and requires no adjustment upon tube replacement.

The pi-network output circuit matches a relatively wide range of load impedances by switching both inductance and parallel capacitance with a single rotary switch. The amp has switch positions for 10m-15m-20m-40m- and (3) ranges for 80m. The amp tunes and loads easily although the variable caps are not equipped with gear reduction drives so loading on 15m & 10m especially takes a bit of tweaking.

With respect to reliability, the only other problem I have encountered was opening the output circuit a few times which was my own fault for being a bit too aggressive on the power running RTTY. The first time was one of the anode connections, the second was a solder joint at the coil tap. Both were easily diagnosed and repaired.

I have read where some folks have replaced the 811Aís with 572Bís. I have personally never tried this because Iím donít feel the power supply is adequate to really take advantage of the higher 572Bís rating, nor do I think that the incremental output gained would be worth the risk. I have used the amp regularly for about 6 years and it now serves as a backup. The amp is useable on the WARC bands by selecting the closest frequency. The purchase price was an even trade for a vintage CW transceiver valued at about $200.
 


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