I replaced a 10 or 15 foot piece of rg8m with a 20 foot radio shack regular audio cable. This went between the berringer on the desk, to the nikko power amp in the rack (now empty and out of the way). The rack will hold the homebrew pair of 4d32 rig in the future.
The level was the same except for the extreme highs, which jumped from 20% modulation to close to 100% with the radio shack cable. This was from making loud s sounds into the mike. Doing more checking, I found I had put bypass caps in the audio power amp, both on the input, .047 uf, and the 8 ohm output .01 uf. These were likely to large, and along with the coax, reducing the highs. There was a large change between the coax and the regular audio cable when I tried that first, but its very likely it interacted with the bypass caps and pushed the roll off frequency down to 3000 to 4000 hz??? I changed the caps to .003 in that amp, and also bought 2 new amps, a one rack mount space 20 watt per channel symetrix amp, that seems to need no RF bypassing at all, and a samson 60 watt per channel amp, also one rack mount space (nice and small). It was mail order, and has not got here yet. The 20 watt symetrix (pawn shop special) works fine on the 811a mod deck, and the 4x150a mod deck (ab1), but does not have enough power to drive the push pull parallel 100th mod deck, it gets up to about 90% mod at the symetrix clipping (20 watts). I likely need to change taps on the driver trans to get more voltage, 4 100th tubes should take less than 20 watts drive... My ears are no good, but I think it sounds much better than it used to, much less high boost for the same sound (in my ears). I guess the 120 watt per channel nikko amp will be a ham fest special, its worked great for 20 years of abuse, has nice analog meters on it, but its quite large and heavy for the shack. I like having all the audio stuff close together on the desk, the berringer mike amp/compressor/eq/etc, the power amp, the tape deck, and the receiver audio amp (marantz). With a one rack space berringer, and a one rack space audio amp or two, you can drive a bunch of modulator grids in a very small space. High quality audio in about 4 inches of total rack space! I paid $90.00 for the symetrix, $180.00 for the (new) samson 60 watt per channel amp. And yes, I still have the good tube audio in the 32v3 transmitters, so I am not a total sell out. I hope to build up a nice tube mike and line preamp/mixer/eq/ compressor/power amp to drive the various homebrew rigs. A tube compressor that works well might be a bit tough though. I have bunch of nice balanced 600 ohm to grid hi fi type transformers that need to go in something. A pair of KT90 tubes will do 160 watts in AB1, very low distortion. Tone control circuits are in the back of the RCA receiving tube manual, along with the mike preamp and mixer circuits. That and the homebrew RF vfo/exciter/driver are all that is left to have a completely home brew station from mike jack to antenna. (can you home brew a mike?) I heard the first part of the article on the second homebrew receiver is in Electric Radio this month, but have not got my copy yet. I have no idea what pictures they used, I sent in a whole mess of photos of various things in the shack. Brett N2DTS
