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Double Bass Polytone:old vs new?

lefty1979

lefty1979

Supporting Member
Mar 30, 2008
331
581
DFW, texas
#1
Posted this over on the BG side, but I know alot of upright guys dig polytones so I thought I'd ask here as well.

I'm looking at a few polytones. I've only played through the newer stuff and I like it, but I'm curious how the older ones stack up. I've played through a Mini brute IV (2 ch, reverb, 15" speaker) and this afternoon I'll probably check out a Mini-brute II (same as the IV with a 12") I know the older ones were a lot simpler, but has the sound changed at all? My local repair guy says the older ones were made better, but that all of them are a pain to work on. That right there makes me lean toward the newer ones (hopefully less problems from newer gear, right?) but seeing as the older ones are simpler designs (1 ch vs 2, no effects like reverb, distortion, etc) they might be easier to fix if something did go wrong, right?

Sorry for the rambling. Anyone with polytone experience, especially anyone that can compare/contrast the older ones with the newer ones, please chime in.

Thanks,
Sean
 
#2
I have one of the old MiniBrute guitar amps in my basement, as I was trying to fix it for a friend. It is stone dead. There is a specialized IC in the power amp that is obsolete and can't be replaced. (I searched high and low on the gray market). Also, the construction is typical for the time period, i.e., nothing to write home about. Maybe I will dig out the entrails and take some pics.
 
#3
I can't advise you on the newer polytone's in contrast... but by guitarist plays an old 15" polytone. I've played through it on many occasions with my DB and EB and loved the tone. His amp keeps on tickin' and has only needed a pot cleaning here and there over the last 8 years of giging.

YMMV, but buying an older one in good shape seems like a good investment to me.

Pat.
 
#4
Thats kind of what I'm thinking. I've got a line on 3 old ones and 2 newer used ones. The older ones are all pretty cheap, but they all need various levels of work, from a simple pot cleaning to major repairs. The newer ones seem ok, but the MB II I'm looking at was owned by a guy that totally abused a Dr Z guitar amp (traded both to the same store) so even though t looks good, there's no guarantees.
 
#5
fdeck said:
I have one of the old MiniBrute guitar amps in my basement, as I was trying to fix it for a friend. It is stone dead. There is a specialized IC in the power amp that is obsolete and can't be replaced. (I searched high and low on the gray market). Also, the construction is typical for the time period, i.e., nothing to write home about. Maybe I will dig out the entrails and take some pics.
Click to expand...
Francis,

Are you thinking of the RC4136 quad opamps used in the old Polytone preamps? These are basically quad 741's with their own pinout and are now out of production. There are adapter boards available such as these from Brown Dog: [Invalid or Expired Link Removed]

Several people I've talked to think the amps from the RC4136 opamp era are the best sounding Polytones.

I have to agree the older amps are much better sounding to my ears. They are very low powered by today's standards however, about 50 watts max, and so have limited headroom for all but the quietest gigs. A GK MB150 combo, for example, will play much louder.
 
#6
Ah, sadly the problem is in the power amp, and probably involves a specialized National IC that is essentially a power op amp minus the output transistors.

I will see if the preamp fires up, and if so, then I will scope it out. I remember the 4136 from all of Craig Anderton's circuits, and having to rearrange everything to use the op amps available from Radio Shack. Those were the days.
 
#7
fdeck said:
Ah, sadly the problem is in the power amp, and probably involves a specialized National IC that is essentially a power op amp minus the output transistors.
Click to expand...
Very interesting. I've repaired quite a few Polytone amps over the years and have never seen that configuration. All the older Polytone amps I've seen use an all discrete transistor power amp with no IC's.
 
#8
The chip in question is a LM391N:

Invalid Link Removed

It is possible that I have a later generation Polytone. Note that it's one of their guitar amps. Now my curiosity is piqued, but unfortunately, the amp is buried deep in my garage. I suppose that one could replace the power amp altogether with a little Class-D module, assuming that the tone is in the preamp.
 
#11
I have one of the old mini brute II series amps with the 12" speaker and the black velveteen covering. I'll never sell that amp. It's not nearly as good as the AI/EA stuff for what I do, but the damn thing is older than dirt and keeps on ticking. I keep it in the office at the U., and all the bass players (and some of the guitar players) are always asking to borrow it. It's a one trick pony to be sure, but it's a pretty good trick!
 

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