Sunday, August 18, 2013

The Harmony B3500 Bass Amp

Here's a little bass amplifier I picked up for pocket change: A late 70's solid state bass amp, the Harmony B3500, with a matching cabinet. For reasons unclear to even me, I'm inordinately pleased with this little thing. It's apparently somewhat rare--at least in working order. I haven't unearthed any web photos or documentation.

So the specs are rather unclear, but I can make some educated guesses:

-- B3500 is the retail model number.
-- 7044B-90PB is the factory model number.
-- 35 watt output (EDIT: maybe not. Sucker is loud for a SS amp, could be 50w).
-- Came with optional matching cabinet, 4 or 8 ohm load (Speaker complement? I'm thinking 1x15).

The wattage guess should be accurate--the back label lists the total power consumption at 50 watts (of course output must be lower), while the name itself--B3500--strongly suggests the likelihood of 35 as the magic number. (EDIT: again, rethinking this...might have to hack test the wattage...)

And the speaker load? Harmony sold a sister amp--the L3500--for guitars ("L" for Lead, no doubt). The L3500 had tremolo and reverb, and likely an identical output stage. References to that amp can be found online. Unfortunately they differ as to the cab impedance; sources list both 4 and 8 ohms. One source lists the cab as 2x12, but it's dimensions make that a very tight fit...

The cabinet is missing the original speaker and baffle board, but it's likely from it's size that the original complement was one 15'' speaker. It came with a poorly fitted homemade baffle and a Quam 12C16MI guitar speaker. "MI" for Musical Instrument speaker; apparently Ampeg used them in guitar amps in the late 70's, early 80's. It's painted gold and I have two. I'm fairly curious as to their sound in a good guitar cab. I have a 1950s Quam speaker in my Lectrolab R600 which has a very cool sound, but it has only fair efficiency--not surprising really, for the era.

The cabinet certainly belongs to the head--the width and tolex are identical. For now an old 100 watt Utah 15'' speaker will be fitted to the cab.

It's clearly dated to sometime in 1979. Here's the back of the head. I've redacted the actual serial number, but it's in the 05xxxx range.

As a Harmony product produced in 1979, this amp originates in a "shadow period" of company history. Harmony ceased operations in 1975. Originally founded in by Wilhelm Schultz in 1892, Harmony functioned continuously as a business until that year. Post 1975, Harmony seems to have undergone several incarnations--reportedly as a brand name for Asian-made musical instruments and accoutrements. However, there were a variety of owners and management over a 25 year period until 2000. At that time the name was acquired by M.B.T. International. The Harmony brand was purchased by the Westheimer Corporation in 2009, it's currently owner / operator.

Any additional information about the company during the era of these amplifiers (1979-1982) would be appreciated...

The internals are compact, as early solid state amps often are. The output stage is an NPN / PNP push-pull pair.

Note the fancy script "T" on the PCB. My old 70's Thomas Organ wah pedal has the identical manufacturers mark. I need to track that down...

Despite my dearth of experience with bass amps (I haven't really played bass since the early 70's), I find myself really liking the amp. I acquired an old Peavey Forum bass a couple years ago and it sounds very nice through the B3500--much better than running it through any of my guitar amps. It's punchy but not distorted (up to 9, anyway--and maybe that's 'cause I'm using a guitar cab until I fix up the Harmony cabinet). Sure, it's not loud enough for a rock setting, but it's not too quiet either. 

Anyone else have a Harmony B3500? Or use one back in the day? Drop me a line...


  1. I picked up one of these without the speaker cab a short time ago at the Goodwill for $5. It was marked "non-working." Took it home and opened it up. It had a capacitor that had lost a bit of solder and come loose. Also the fuse was burnt out. After about 10 minutes of fudging with it I put it back together and plugged it in to my little Univox 1x15 bass speaker. I'll be damned if that lil' sumbitch didn't fire right up and sound like gold. Pretty loud as well. Very nice sounding little amps. I also plugged it in to a little 1x12 Quam speaker that I had lying around and tried my guitar with it. They are great little solid state jobbers. Kinda wished that I would have kept it, took it to the local shop and they gave me $90 store credit for it though. Saw it priced at $179 the other day.

    1. Cool, thanks for the comment. I love an easy fix...

      I've repaired the cab, adding an old 15' Utah speaker. Sounds great with the amp. I'll need to update the page--I'm beginning to wonder if these aren't closer to 50 watts, it is loud for sure, like you said. Gets a little hairy above 9, though.

      I'll make a new post, I also added a three-prong cord plug (computer style) to the back of the B3500. Had to upgrade it to a grounded cord anyways; thought I'd add the plug recepticale since it's not very collectable (just a cool sleeper).

    2. I have one that is in mint condition. I got it with a cabinet containing an Eminense 15". If anyone is interested in buying it call 580-482-3239 and ask for Jack or leave message.