Also noticing that MM HD130s are surprisingly affordable on ebay. There seem to be 2 versions - the standard HD130 guitar/bass version and the HD130 reverb. From what I can tell the only differences (other than the reverb/trem) is the channel 2 bass EQ cap (and therefore the corner freq of that tone control - mid and treb tone controls look the same, as is the bass cap on Ch 1) as well as having a Deep vs Bright switch. The rest looks pretty much the same, though some things are laid out differently. Anybody got any opinions of how much difference this makes - that deep switch useful or just mud city (the bass cap is easy enough to change out)? Does it do anything that can't be achieved with the EQ? I'm cool with the ss preamp.
I´ve had a HD130 since 1993, it´s a great amp when you get to know it. I spent a few years finding speakers for it (see other threads) but eventually found a 212 and a 115 musicman cabs, the 212 i put neo´s in and the 15 i put a reconed EVM15L in. Love it.
A note on the eq, as you say the 2 channels have only cap differences, but they sound really different. The bass channel is a ´bass cut´channel, and in most cases this channel sounds best for bass guitar. I think the general eq opinion on HD130´s is to use the bass channel with the deep switch engaged. I like that best too.
The switch is as you see from the schematics just a large cap in series (between the preamp and the driver) but it really gets things deep. It does things the preamp cannot. I found it useful when experimenting with cabs too. Another thing, I put a preamp in jack on it, so if i need to have a lot of gain (don´t like the ´drive´sound on musicmans) I just use another preamp. Power enough.
Another note, I have the tube driver version. I know they changed to solid state driver for reliability reasons, but I have had quite a few musicimans on the workbench over the years (seems to be a lot of them here in Norway) and never had any tube driver related troubles. But i have repaired maybe 3 or 4 solid-state drivers. As a side note all of those had stock caps in power supply, so maybe the tube driver handles PS issues better. Quite a few with arced sockets too (high voltage here) but fresh caps and sockets and these amps are very reliable. Good sounding, with some personality.
If you want to, you could set it up with 6550 and probably have more headroom. I did think of doing that myself, but if you have a strong EL34 set it delivers nicely. You will have to use a set that actually handles 800V, though. We have 240V in the walls here; when these amps were made we had 220. These 20V turns them into monsters if you have no bucking transformer!