RM50B Price?

Thinking of getting one, but wanted to check with some of you on what would be a reasonable price for a used RM50B.

Thanks in advance
FM

When I first decided that I wanted an MTS my heart was set on an RM20B, But I ended up with an RM50B. I paid $379 +shipping for mine on ebay. It was up on a buy it now price of $450 and I got it for the lowest price because nobody else bid on it. Shipping ran about $40 I tihnk and it weighed in at just above 80 lbs with all the packaging.

I don't see very many MTS amps on ebay anymore, at least not as many as I used to. I think they are really starting to cactch on. Most of what I do see are RM100 heads that go for $800-1000

I think that the RM50B is the best value to get into the MTS system. RM50HB heads go for at least $100 more and you still have to buy a $200+ cabinet. I've also seen RM20B's go for nearly $500. The RM50B is the exact same amp as the RM50HB, its just built into a combo frame with a speaker. If you want you can unplug the built in speaker and use any speaker cabinet you want. The speaker out jacks are right on the back of the amp and you also have an impeedance selector swich so that you can use cabinets that are wired for 4,8,or 16 ohms. Just make sure when you get your amp check to see if that swich is set at the right setting. When mine came it was set at 8 ohms and I just assumed it was correct. I couldn't figure out why it sounded so crappy. I figured maybe it was the power tubes and while I was changing out the power tubes I saw a sticker on the bottom side of the magnet that said "16 ohm speaker". I've talked to a few people who also had this problem and I think someone also said that the manual says the speaker is supposed to be 8 ohms.

Well I received my RM50 today w/ a Recto, Tweed, Ultra, and Modern Module only had a little while to play it but so far I am impressed. Thanks for the info. BTW I also noticed that the unit was set to 8 ohms and the speaker was labled 16 Ohm. The manual also stated 8 ohms as the default. I measured the speaker with an Ohm meter and it said 8 Ohms, but that was with the speaker connected to the amplifier. When I removed the connection and measured the speaker it measured 16 Ohms. I guess in the factory they measured the speaker with the amp connected and thus the documentation as well as default setting were set to 8 ohms (go figure). I am going to verify this with Randall.

FM

Hey, a couple points to your post:

I bought my RM50 for $540 (shipping included) with 3 modules on ebay. Probably could have been cheaper, but I turned one module for $120 and so it cost my $320 - heck of a deal!

For measuring the speaker impedance, it is always done with the speaker disconnected from the amp. From electrical theory, for maximum power transfer, you match the load impedance (speaker in this case) to the generator impedance (the amp's output transformer in this case). Actually you match it to the the complex conjugate of the impedance but it can be simplified here.

So, for an 8 ohm speaker, connect it to an 8 ohm impedance secondary on the transformer. The same for other impedances (4 to 4, 16 to 16). A 16 ohm speaker connected to a 16 ohm output impedance looks like 2 16 ohm resistors in parallel = 8ohms.

Additionally, the transformer is designed to be damped properly with the right load. If you put the wrong load (ie: wrong impedance) there will be ringing in the transfomer - translated as a bad frequency response characteristics and/or bad transient response.

Not sure about this point, but my guess is that the ringing could induce oscillations, which at high enough voltages could damage components leading to damage to the amp or heat in the transformer causing damage. Let me check on that point

Way more than you wanted know :wink: