[MrFixr55]

My guess is that subbing L 11 with a resister will increase frequency response at the high end, but may add too much RF through causing distortion. That can be be taken out by paralleling the interdtage transformer with a cap, maybe 300 pF? Subbing L12 may not have much effect as it was emoved from the next version.

[radiorich]

Hello Mike,
Far as that tone control that was a great save and some smart thinking on your part .

Yes, AK radios are not for the light hearted I think a lot early sets are tough like my General Motors console and I do have one AK in my collection model 85.

Sincerely Richard

[morzh]

Rich,

AK was the firs, or one of the first to pioneer (not all pioneering is good ) using rubber-coated wires. Otherwise they are not the worst. Cap cans, yeah...but then early Philcos with their large tin cap cans are nasty in their own right.....

The stinkier the manure, the sweeter the fruit

[morzh]

MrFixr

The L-12 choke is a plate power filter, and in R-73-A it is replaced with 20,000 ohm resistor. The inductance here is not a part of the output characteristics of the driver circuit, so I think I might just do exactly that - put 20K resistor instead.

The L-11 is different.It is air core, and I cannot find anything like it being sold.

[morzh]

Replaced some more resistors.

I only need to replace L-11 choke. Need to find an info on it. I, of course, could try to calculate the inductance, very loosely, but this won't help me much. I could replace it with a cored inductance and a resistor, of course, if I know what inductance it is.

[radiorich]

Hello mike,
for sure and sounds like your coming right along on this radio this weekend I worked on an Arvin !

Sincerely Richard

[RodB]

Hi Mike,

I think you're OK with, just 20k plate load resistor. I'm pretty sure the rf choke/resistor combination in the plate circuit is to suppress ringing. I remember it being used in the old TVs. I need one for each ear, stops the ringing.

[morzh]

Rod

If you refer to the RF choke (L11), yes, you are right, though I am not sure about the ringing. Ringing usually is suppressed by snubbers, but here we do not have very fast transitions, and if anything, inductance is not a very typical component to help with ringing.

L12, well, it is the filter, so, yes, quite replaceable by a resistor, considering the 1uF is already there, and in R73A the same cap is used with 20K instead of the choke. Then there is another 20K plate load.

I will try to find that choke, or at least calc the inductance, and see what can be done. Worst case, yes, a resistor will do.

[morzh]

Found a bobbin coil calculator, that from the geometry and the resistance came up with the same number of turns (10% accuracy) that I calculated the coil had.

From it, the inductance is on the order of 7H.
So, unless I can find a bobbin one, I will have to resort to a Hammond cored inductance. And then add a resistor.

[morzh]

This is the calculator.

   

[RadioSvit]

Michael, I think that the choke L11 is used to increase the reactive resistance of the anode load for the lamp of the input stage due to its high internal resistance, because as you know, the inter-stage transformer needs a more powerful driver tube than the one used in this radio. In my opinion, the frequency response correction function is secondary here.
PS... I hope that Google will translate it correctly and you will understand what I want to say

[RadioSvit]

In other words... This choke helps to match the high internal resistance of the radio tube with the significantly lower reactance of the primary winding of an interstage phase inverter transformer, as it doubles the inductance and reactance.
Without this inductor, the level of harmonics will greatly increase and the return at low frequencies will decrease (if you put a jumper). If you put a resistor of 3 kΩ, then the signal level will drop significantly

Другими словами ... Этот дроссель помогает согласовать между собой высокое внутреннее сопротивление радиолампы с значительно более низким реактивным сопротивлением первичной обмотки межкаскадного фазоинверторного трансформатора, так как вдвое увелоичивает индуктивность и реактивное сопротивление .
Без этого дросселя сильно увеличится уровень гармоник и снизится отдача на низких частотах ( если поставить перемычку ). Если поставить резистор 3 ком то сильно упадет уровень сигнала

[morzh]

Peter

Yes it translated well. Thanks. This is why I felt I wanted this choke to stay. L12, on the other hand, is not that important.

[MrFixr55]

Hi Folks, 

7 Henry sounds to be way too much.  How many Henrys (Henries?) is a power supply filter choke, 30 maybe?  With a 7 H choke in series between the 1st AF and the interstage transformer, this thing is gonna have a frequency response of about 30-300Hz (yes, 300.)  I may be wrong in my guestimate here, and my college Physics II textbook is buried in the garage (archeological dig), but I have a VEC 1290K AM Transmitter kit, with a rather clever way of modulation.  The output of an LM386 is directly connected through a 1000 uH (micro-Henry) choke, to block the RF from the Audio Output, which is actually the B+ for the Transmitter final, hence the coupling only by a choke, no cap in series.  The Schematic is attached in case this whets someone's appetite).

So I think the choke should be in millihenries instead of Henries.  I don't think any harm would come by just trying the resistor, especially since this part is not in later sets (OK, it is in the 73A, but other sets that have push pull and interstage transformers, I think that this part eventually disappeared.  If it sounds horrible, then try to find the right inductance.  There is inductance to the transformer to begin with.


Maybe that 7 H choke will fix the ringing in my ears but the high frequency response of my hearing is bad enough!   Ms Fixer is always )!$$ed at me every time I ask her to repeat herself.

Best Regards, 

John,

[Chas]

I, am not surprised at the value of the choke in detector service. The "audio coupler" in a SW-3 has a very high value choke. Then, again, it is in a different style of detector, grid leak, regenerative.

IMHO the RCA engineers certainly did not "over engineer" the detector circuit and planned for a reasonable fidelity from the radio.

If the choke is iron core and layer/parallel would it is not all that difficult to replicate. An alternative is to hack an interstage or an output transformer primary, by ignoring unused winding or "ripping" it off. If that interstage does not yield enough Henry's, series the primary/secondary.
If the winding is "universal" that can be done with a Morris but with wire that has been waxed... Subbing another "type" of component will not give the results desired. If that were true RCA their bean counters would have done it...

Chas