Tram D201a

[HiDef]

I think what some people miss here is that these resistors are not just voltage dropping resistors. They are part of the Heising modulation circuit used in the radio. These resistors have an electrolytic cap across them for a reason. The resistors reduce DC power to the tube while the cap allows the AF modulation power to pass through without reduction. The overall effect is reduced carrier and increased modulation.

The D201 is not Heising modulated. The lytic across those 2 resistors keeps the resistors from wasting audio power. They only waste B+.

You are correct that the final will exhibit more drain from the xfmr by just bypassing the resistor. The plate load must be reduced (more capacitance) to where the plate dip will only give 12 watts out the pipe. This reduces plate current and most likely puts the rig where the modulation transformer ratio is optimum. It also puts the load on the power supply right back where it was at 4.1 watts out. The increased audio power needed to modulate fully will use more power but it's less than 10 watts at low duty cycle.

The compressor must be re-adjusted to obtain just under 100% negative modulation after confirming correct audio polarity. If it's only done on the bench with an audio oscillator the job isn't finished.

I've always wondered how these rigs were ever type accepted. Maybe the ones built at the very end needed to be changed to continue certification. I didn't know they changed the final toward the end. Interesting.

 

[packrat]

Yes, I agree that they can be made to make more power, but like I said before, it WILL kill the radio. Maybe not today, but soon. All that extra power produces extra heat. No way around it. Not a matter of if, but when. Heat will cook the already trouble prone, 30+ year old circuit boards, lift or burn traces, and cause all kinds of cool smoke. This is really why I still have my handwired D-201.

PR

 

[Shockwave]

It seems as though I have misspoken about Heising modulation in the Tram. Without a modulation reactor this is not Heising. What I should have said was that the cap and resistor in the Tram form the same circuit that is used with Heising modulation to increase the audio level.

Hi Def, don't you mean less capacitance to reduce load on the final amp? Adding load capacitance after increasing the plate voltage will kill the peaks. Besides, changing the plate voltage on an RF amp does little to effect it's output load impedance because voltage effects current proportionally.

This is why Heathkit use to brag about being able to switch from tune mode to SSB on the SB-220 without having to retune. They simply cut the B+ by about 30% in tune mode and the current automatically goes down by 30% for the same drive level. This means output load impedance has not shifted.

Can I respectfully disagree that shorting the voltage dropping resistor will draw more current from the power supply at 12 watts output then 4.1 watts regardless of how you tune the PA? We certainly haven't increased the PA efficiency by 300% so the only way around that fact is to draw more power.

As far as certification, I'm nearly certain that many of the changes we see in the D-201A are as a result of Tram needing to keep that certification. The smaller output tube, smaller transformer, added 10 ohm resistor, and screwed down lid are just a few.

At the end of the day, it is a better idea to leave both of these resistors intact. While the Tram does have headroom to make more power, any good tech will tell you to leave that headroom there to reproduce audio peaks. That is the reason the Tram has such a good following with it's audio quality.

 

[HiDef]

Class C R.F. amplifier with Pi net reducing the load capacitance will increase the load and current drawn by the tOOb. It does look incorrect but that's how it works.

With class C you can load heavier or lighter looking for a certain load impedance to match a modulator. Class B is usually loaded for max smoke.

Yes, I'll agree that more power will be drawn by only bypassing the resistor without reducing the load. The radio will also make more than a 12 watt carrier before changing the loading. I have one here and really don't remember which resistor has been bypassed. What I do remember is the modulation percentage at 12 watts. It's fine. My point is that the resistor will waste 10 or so watts in heat which can be applied to the final. Done properly it won't make your radio fall apart or cause itching and burning.

Another thing to look for if modulation percentages fall off is lack of grid current in the final. Wimpy drive can be one cause.

Question: What color stain is a match for the woodgrain sides?

 

[MisterFatty]

Quantity does not always equal quality... with the ready availability of outboard amplifiers, and the small gain, I see no valid reason to run the old radios beyond 6-8 watts carrier.

To each there own I guess....

 

[HiDef]

I'm talking about a mod I came up with well over thirty years ago.

Again, If your D201 cannot make 50 watts P.E.P. with a 12 watt carrier there is a problem somewhere.

12 watts is a nice drive level for an SB220. 4 isn't.

See you when 10 meters opens.

 

[packrat]

Well, that is why God made Kenwood!

 

[Dealer]

Class C R.F. amplifier with Pi net reducing the load capacitance will increase the load and current drawn by the tOOb. It does look incorrect but that's how it works.

With class C you can load heavier or lighter looking for a certain load impedance to match a modulator. Class B is usually loaded for max smoke.

Yes, I'll agree that more power will be drawn by only bypassing the resistor without reducing the load. The radio will also make more than a 12 watt carrier before changing the loading. I have one here and really don't remember which resistor has been bypassed. What I do remember is the modulation percentage at 12 watts. It's fine. My point is that the resistor will waste 10 or so watts in heat which can be applied to the final. Done properly it won't make your radio fall apart or cause itching and burning.

Another thing to look for if modulation percentages fall off is lack of grid current in the final. Wimpy drive can be one cause.

Question: What color stain is a match for the woodgrain sides?

___________________________________________________________________________

Cherry Oak or what is referred to as Gunstock...

Remember that those are Laminated..

John

 

[HiDef]

Thanks John.

 

[Warlock35po]

MisterFatty, AMEN Bruddah, Warlock35po.

 

[idjjoker1]

hey guys i have a d201a i have been fixing , i got everything back transmitting but the s-meter is still not right . i have the negative voltage at the meter thats it . is there a common problem , any suggestions?

 

[Shockwave]

In the Tram D-201 series radios the "S" meter is driven by a pair of 6GH8 tubes. First confirm the "S" meter is not pinned against the left hand side. If it is, adjust the calibration control near the relay to zero the meter with no signal present. If that's not it check the two tubes. If that's still not it you probably have open resistors or shorted caps in the circuit. The Tram is noted for having resistors that feed B+ to the tubes open up. Mostly on the SSB 6BA6 IF tubes and not the meter. I may be wrong but I think they added some solid state parts in the D-201A meter to help stabilize it and that may also be the problem.

 

[sir. witchback]

I got 3 trams now.

Well, I got 3 trams off my brother, (2) D201a's, and one d201. None of them are powering up, but im working on one now. They all seam to be very nice radio's, and I will try to keep you all posted on my working with them.

 

[Jimbo165]

I just picked up a 201a is there anyway the channel selector can be fixed or possibly taken partly apart to spray some contact cleaner inside. Mine is acting up on channels 31 to 35. As many 201a out there seems like someone could come up with a fix???. Thanks

 

[MarkIV]

Packrat makes a valid point however it only applies to the D-201A made in Mexico. Just before Tram went out of business they tried to cut costs. The core on the power transformer used in the last radios made was 33% smaller in size and 33% less powerful. Evidence of this is found by looking at the power output stages of late model radios. The final tube was stepped down to a 6DG6 and a 10 ohm resistor was added at the final tube socket to reduce output.

This is certainly not the case with the older D-201. The radio was a powerhouse with a 6L6 modulating another 6L6 and a power supply with plenty of headroom. These tubes are about four times higher plate dissipation then the 6AQ5 or 6BQ5 used in any other CB output stages. With this in mind I have to disagree with this radio being built without extra headroom.

Most failures in the D-201 are related to the old carbon resistors changing value, filter caps drying out, and tubes gone bad. All of these problems can be greatly reduced by installing a small fan on the back of the rig. I can't count how many Trams I've seen over the years with open resistors in the B+ line feeding the SSB IF RX tubes. I can count how many I've seen with a blown power transformer. It was a single D-201A in decades, made in Mexico.

I suppose it really comes down to what you are doing with the radio as to if you should mod it to do more power. For example if you're driving an amp, 2 or 3 watts either way could make a huge difference in output, while being barefoot this power change means almost nothing. An old Tram with the full sized power transformer can easily make twice the rated carrier and still 100%modulate it without stress.

Ancient post and incorrect. The D201A’s power supply was of a different design with the same output. It did not need to have as big. 2nd, the 6DG6 while not as robust as the 6l6 forvthe final actually gives more peak audio output and always sounds better when used as the final in this radio.