Ranger Modulator Help...

[kx9dk]

Almost finished refurbishing an early version Ranger and having trouble isolating a problem in the modulator.
I've modified the modulator using the WA1HLR mod found on the AM Window site. http://www.amwindow.org/tech/htm/rangmod.htm

Whenever I put the function switch in the AM position the modulator tubes (6550's) take on a faint blueish glow (down towards the bottom of the tube) and I hear a faint hissing sound. Rig loads up ok with plenty of output. The best modulation I can get with a 1 Khz tone is about 60-70%.

Anyone have any ideas what is happening here?

Eager to get on AM.

Thanks,
Dave
KX9DK

[w3jn]

Spunds like you have an ultrasonic parasitic somehwere.  Get in there with a scope and see what's happening.  You might have miswired something or got the neg FB loop hooked up backwards.

73 John

[Tim WA1HnyLR]

Dave, On the Ranger mods there have been a few upgrades since I did up the one that the article is about. Due to instabilities of the 6550 the grid resistors,(R18 and R19)have been reduced to 68K .The audio coupling caps are upped in value to .5Mfd caps. R 11 is fed from the full HV B+ not the LV B+. Wattage ratings of the resitors are bumped up to 2 watt rating. This gives more headroom to the last audio stage and phase inverter. Recheck your work. The bias on the 6550 s should be set to idle @70-90Ma. The bluish glow is nothing to be concerned about. You should be able to make plenty of modulation. If the modulator is pulling mass quantities of plate cuntrent and not modulating very fully you may have a blown mod transformer. Disconnect the negative feedback winding and observe how the modulator behaves. If the gain goes up when the feedback winding is reconnected the phase needs to be reversed .Either reverse the leads of the feedback winding or swap the leads on the plates of the modulator tubes. There are far better mod transformers than the stock Ranger modulation transformer. The Ranger mods MUST be done in their entirety ,not just the modulator circuitry. The power supply modsand push to talk control circuts are equally vital to the operation of the transmitter. Good luck with it De Tim WA1HnyLR

[K1JJ]

Watch the Tron "Pimp Your Ranger", caw mawn.   

[WA3VJB]

Hey Timmy where'd you get the AVATRON ?

[The Slab Bacon]

OR DID YOU MEAN SLIMATRON??

[kx9dk]

Tim,

Thanks for the updates to the modulator circuit. I'll make the changes and let you know what happens.

Thanks,
Dave
KX9DK

[W1GFH]

Howdy,

Been out of the loop for a while. But I did surf across this page, which seems to have some blasphemous ideas regarding the accepted "ranger mods".

www.w8ji.com/Johnson%20audio%20mods.htm

Joe, W1GFH/6

[K2FW]

Dave, On the Ranger mods there have been a few upgrades since I did up the one that the article is about. Due to instabilities of the 6550 the grid resistors,(R18 and R19)have been reduced to 68K .The audio coupling caps are upped in value to .5Mfd caps. R 11 is fed from the full HV B+ not the LV B+. Wattage ratings of the resitors are bumped up to 2 watt rating. This gives more headroom to the last audio stage and phase inverter. Recheck your work. The bias on the 6550 s should be set to idle @70-90Ma. The bluish glow is nothing to be concerned about. You should be able to make plenty of modulation. If the modulator is pulling mass quantities of plate cuntrent and not modulating very fully you may have a blown mod transformer. Disconnect the negative feedback winding and observe how the modulator behaves. If the gain goes up when the feedback winding is reconnected the phase needs to be reversed .Either reverse the leads of the feedback winding or swap the leads on the plates of the modulator tubes. There are far better mod transformers than the stock Ranger modulation transformer. The Ranger mods MUST be done in their entirety ,not just the modulator circuitry. The power supply modsand push to talk control circuts are equally vital to the operation of the transmitter. Good luck with it De Tim WA1HnyLR

Timmy, of you feed R-11 from the HV supply instead of the LV, won't you also have to change C-8 to something larger then a 450vdc rating?