Thanks again to Chuck for providing the 198/a docs. They are posted.
I acquired a couple of Tiger .01 amps and a 198 preamp. The amps sound fantastic but the pre suffers, in my opinion, from too many pots and connectors. The balance slider is rough, sticky, and actually does nothing. The op-amp connectors are noisy and I suspect the cheap CTS pots will too. I am hoping that Deoxit will solve all the noise, etc. If not I’ll be direct wiring the works. Does anyone have experience/thoughts on this?
I had to replace the big volume control on mine, but that was back when I could still get parts from SWTPC. Yeah, the mechanics of this preamp were a weak point. Never had much trouble with the little lever pots on the PCs. I’d douche everything with a tuner cleaner with lube and save the expensive Deoxit for known trouble spots afterwards.
Mine is a real early one with lots of wear and tear and was left open and unused for a while, when I tried to use it recently it is all FUBAR and needs to be gone through. For decades I’ve been wanting to make my own better preamp from scratch but using the better ideas from this unit. A project I hope to finally get into when I take early retirement soon and clear out a few more urgent projects first.
My 198 A preamp appears to have a problem. When coupled to my 215A power amp, I am not getting the same level to the speakers. This is indicated as well by the meters on the front of the 215. Right side is considerably lower. The reason I know it’s the preamp is because I ran the power amp with a different preamp and all is well.
The balance control is positioned in the middle, but there is a problem with it. It won’t slide, unless I get behind the button, to the slide itself, right near the actual slide pot.
Which pots on the boards in the preamp can I adjust to possibly remedy the situation?
There are pots located right by both the input and output connectors. Does the balance issue change with input change? If so adjust the pots by the affected input, otherwise the pots by the output connectors. Just set L&R pots so they are physically in the same positions for now. If you still have the issue and you think the balance control is damaged, unsolder and tape off the wire s on each end to eliminate it. If you still have issues and the unit hasn’t always been stored in a clean dry area, then you may need to clean the switches. Get a can of tuner/ control cleaner WITH lubricant (silicone) . I do this with it on and music playing but with the output controls or the power amps input controls turned down to a low level but to where I can still hear if things are changing. If none of this helps, then move on to the four gain cards, but play with those with everything powered down. Two of them have pots on them but these are for offset, not levcl, refer to the text, but those are not your issue. Pull out one at a time (to avoid mixing them up) and clean the connector and pins with the same spray. Beyond all this you can reverse the pair on the input selector board and then see if the low channel stays the same or swaps Left and Right, and then likewise do this test on the tone board, remember to shut off the all the power between swaps.
I love my 198/A! The balance pots have that problem, it is a design flaw. To move mine I have to open the cabinet and use a jewlers screwdriver to move it from the base of the knob post! Some day I’ll replace it, but I almost never use it.
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