The AM Forum

I have a Ranger here that I want to do the following mods on. Any help will be appreciated, I like to listen to others ideas.

Of Course, Add PTT using a good quality relay that not only handle the PTT but turn on the Red Led at the same time, and do any power supply switching that might be recommended.

Replace the OA2 in the VFO with a Zener

Ive already removed the 18K and put it inside the chassis and its rated
25 watts ( just cuz I had it )

Possibly replace the stock filter with a filter string and equalizing resistors or whatever

get rid of the tapped heat generating bleeder/divider resistor.

Increase the drive on 15 and 10

idea's fellows?

Ronnie - W5SUM

The bottleneck in audio response is the driver transformer.  It will perform much better if you take the DC off the primary.  Put a 1 mfd capacitor in series with the primary (doesn't matter whether it's inserted at the plate or B+ end of the winding).  Find a 30K 5 watt resistor, connect it to the paralleled plates of the driver stage, and return to the HIGH VOLTAGE B+ (the increased plate voltage will compensate for the voltage drop in the resistor).  The low frequency response and phase shift distortion should be improved, since the transformer is no  longer being saturated with DC.

When I had mine, I went a step further.  I removed the driver transformer, took it apart and removed the laminations, restacked the laminations like a power transformer (cross-laminated) by alternating the positions of the E and I sections of each adjacent  lamination.  Then I reassembled the transformer, and after I replaced it in the circuit I measured frequency response.  It was flat to well below 50~.

Note:  I am recalling this mod totally from memory of what I did some 30 years ago.  If there is not enough audio, measure the plate voltage on the parallel 12AU7 sections (or was that a 12AT7?).  If it is considerably below normal, try replacing the 30k resistor with a 10k.  I think I used a 30k, but it was possibly a 10k.  I recall using trial and error to determine the best value of plate resistor.

ur right, its a 12AU7    klc

...thanks Don, I often wondered about rebuilding/replacing that driver xfmr. Wonder if there may be a drop-in replacement. Anyone know the stock driver xfmr specs?

I believe the P-T124E (Hammond 124E, ~25$) from AES is a drop in some people have used to improve the Johnson audio chain. Havnt gotten around to it myself so cant say if it's effective or not. The tubesandmore.com web page spec says 50hz-13khz, but the spec on the box of the one sitting here in front of me says 150hz-15khz???

Larry

That's probably the spec with DC running through the primary.  The partial saturation of the core from the unbalanced DC effectively reduces the amount of iron in the transformer, and thus low end  response.  That's why most broadcast modulation transformers are designed for use with a reactor to take the unbalanced DC off the winding.

P-T124E is a VERY nice driver iron for both Valiants and Rangers (Viking s too)
I 've used these in several ...remember to install it "backwards"  in the circuit!!!

I've used it in a single ended driver stage with 12AU7 in parallel and also
PP 12AU7 ....frequently, I will block the DC in the single ended config tho....and
feed the Parallel 12AU7 via a series resistor....fyi
73 steve
8tow