Tram D201 Advice on transistor between FL2200 & T201 where L203 should be

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      AX005
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        Frank Woolfe on facebook 2018
        7 January at 04:52 · Port Augusta, SA
        Looking for advice on this transistor highlighted, what does it do??? cant find any info on this between FL2200 & T201 where L203 should be…
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        Wilbert Sheran
        Wilbert Sheran Is this a D201A ??? It’s Q202 and if you consult the Manual on Pg. 28 it shows the Board Lay-Out and then on Pg. 22; the Block Diagram, it tells one what it is… Q202 Transmit Mixer http://www.cbtricks.com/radios/tram/index.htm
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        Frank Woolfe replied · 5 Replies
        Ron Edwards
        Ron Edwards It’s a mod added byh the factory to shunt a carrier to ground on receive. They played around with this circuit for years. Some have a tank instead. Last versions used this transistor, 1k resistor and .001uf ceramic cap located on the foil side of the board. Doing this by memory so don’t quite me on the values.
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        Frank Woolfe
        Frank Woolfe That makes sense, it appears to operative on TX also, the 1k resistor is on the base of this device and cap on the foil side..
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        Ron Edwards
        Ron Edwards There are a few factory changes on the last version fixed bias Tram D201A that have no service notes. I just finished converting, rebuilding a virtually NOS D201 to fixed bias D201A
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        Frank Woolfe
        Frank Woolfe Ron Edwards not a fan of fixed bias due to characteristics of the PA tube changing over time, having the ability to monitor bias/Pa current on the front meter would be ideal
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        Wilbert Sheran
        Wilbert Sheran Most report that Fixed Bias is “louder” and helps one be heard in a pile-up… Plenty of people seem to have made the conversion in order to report the results
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        Frank Woolfe
        Frank Woolfe Wilbert Sheran adjustable bias should really be the way, as different tubes experience different characteristics, setting a bias voltage of say -40 volts for one tube could be 40ma Idle current with another it may be 50ma idle current, not that that is huge in the big scheme of things, and as I continually read and I won’t teach you to suck eggs,, but resistor values change over time, I do like the idea of monitoring Idle current and being able to adjust as the tube ages…just my 2c…
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        Wilbert Sheran
        Wilbert Sheran Frank Woolfe Well, 1 of the 2 D201A Radios I have came as New in 1978 when I bought it, with Fixed-Bias from the Factory… I jumpered the 2 “Power Resistors” under the Chassis with Switches and run the Tram full bore with the same 15 Tubes the Radio came with… The 6DG6 Tube glowing Purple… No problems here… Yes, I did a total restoration a few years ago and I hammer that Radio… It takes a licking and keeps on ticking…
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        Frank Woolfe
        Frank Woolfe Wilbert Sheran well there ya go, I wonder what the idle current on the output tube was??? And how linear was the signal….
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        Wilbert Sheran
        Wilbert Sheran Frank Woolfe I’m just saying the Radio can take the abuse as I have proved it… I don’t think any CBer cared whether I was linear or not or could tell the difference… More often I run the Radio as stock which somewhat abuses the 2 6JG6A Driver Amp that feeds the Heathkit SB 220 Amp… I don’t know how linear the entire System is, nor is it my greatest concern… I am strictly AM as these Radios are not the best on SSB regardless… I’ve seen a Performance Video of what a D201 that is properly Aligned can do, so I assume the D201A is as good https://www.youtube.com/watch?v=pYGYxbXZrcI
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        Tube type CB radio splatter box / harmonics, I don’t think so.
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        Frank Woolfe
        Frank Woolfe Mate What you do is your business and I won’t criticise, yes I’ve seen all these videos saying this iand saying that, Which resistors are you actually talking about as the bias resistors are two adjustable ones that are connected to the cathode there are two one for AM and one for SSB when you look at the circuit
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        Wilbert Sheran
        Wilbert Sheran R642 , R643 which with 2 switches will provide Low (Factory), Medium, and High Output… High being nearly 18 Watts Dead Key
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        Ronald Barton
        Ronald Barton R642 and 643 are plate voltage dropping resistors for the RF final and are commonly bypassed for more watts out in D201’s and quite a few other tube radios that have resistors to drop the RF finals plate voltage. General with the Belly Button and Buddy with the switch pack come to mind. I would think doing more watts with the same modulation power would actually make the signal more linear albeit less modulation. People have been doing it for many decades. Now me since i am a modulation freak, have added resistance there for a lower dead key and higher modulation. Linear no. Loud You bet.
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        Frank Woolfe
        Frank Woolfe Yep, that’s what I thought you were talking about, nothing to do with bias but plate volts, ok to increase for SSB however will decrease modulation in AM mode, More volts on anode = more output..
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        Ronald Barton
        Ronald Barton Well on SSB on that radio it already switches to the plate anode volts power supply directly. Those dropping resistors are used in the AM mode only. However dropping the plate volts in AM will give you a lower dead key / more % modulation while raising the plate volts (bypassing those resistors) will do the opposite.
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        • This topic was modified 6 years, 1 month ago by AX005.
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