The Amp Garage

The chassis I would say is not a one of since the nuts that will tie it up into the cabinet are tack welled in, so the amp started life as something else.

If your looking for any mid boost with aFender type tonestack the only way to get any of that or even get a flat response out of it is to turn the volume way up, crank full up the middle and set the bass and treble very low.

Well it’s got very hard to find knobs from a Heathkit from what I can tell. It’s got a T03 cased transistor mounted near the fuses so I would have to assume it’s DC powered heaters. It looks like it’s got a old paper cased filter in there and 2 other filters that could be old and out of a Highwatt o...

I have used the jtm45 PT in a 65 Fender Bassman and one would be hard pressed to hear the difference with the slightly lesser B+ voltage.

If you can surmount the mechanical difference I say go for it, and you would likely save the owner 100 bucks in the end also.

You did not mention if you tried different known good preamp tubes.

I have had a condition like that a few times that was due to a preamp tube.

Have you tried a different speaker?

Yes they are not at the bottom of the ladder any more.

Note that 6BQ5 PP output stage needs 10 volts less of grid to grid drive signal then a 6V6 output stage does.

Please clarifie what your doing better. You can't be pumping in millamps ( MA ) of signal like you posted, millvolts yes. Interms of the MV level are you saying .037 volts or .137 volts, I use about .115 volts. (-10 DB ) which is about a single coil pick up output level, if your pumping in .137 then...

Of special interest to you if you want to print them off would be pages 31 thru 38.

Note that it only covers tubes that RCA made and there's quite a few that only GE made that will not be covered in detail if at all in the RC30 book.

That wattage rating of any tube is DC parameter, not AC voltage which is the audio output.

Go to the Tubes & more site a buy a copy of the RCA rc30 tube manual, it’s worth every penny as they say!

Here’s a example from the tube data section of the on line Duncan tube amp site.

With a -58 available I would also say that the amp was born with 6550s. With 34s in the amp you want to have the low end of the bias range go down to like-36. Start off with adding in series to the input side of the bias adjust pot a 10k to and then see what that gives you . Of course do this bias v...

If the level of Genius that Designer McIntosh had in him was happy to make a stereo tube amp with its major components laid out like this then suffice to say that you would be fine to do the same for your build.

Golden rule number 1. Whenever working on a amp and especially a customer amp where time is money, alway double check the for the needed resistor value with your ohm meter to confirm what you think your seeing with your eyes. Over the years I have had more then a few that had the wrong color bands i...

You have failing and or bad solder connections on the tube sockets, as such is common with this amp, and I would say at least one bad plate load resistor.

And yes, these amps are a flat out pain to work on!