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67 Bassman Tubes


WRGKMC

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Finally finished re-tubing my Bassman head. I had been running mostly Groove tubes in it since moving to TX about 25 years ago. I started developing issues with a preamp tube crackling, and the bass channel wasn't working much at all so I figured it was time.

 

I later found out I had some bad coupling caps too so I did some replacements on those too so now the bass channel is working the way it should too.

 

Its a great old head which is the second amp I owned and bought it in 1968. Somehow I wound up hanging onto it for all those years.

 

For the preamp tubes I went with the Electro Harmonix tubes for the three 12AX7. The 12AT7 I chose a JAN (Joint Army Navy) NOS tube. It had the best specs and lowest noise on the Tube Depot site and was only $9 so I went with that one for the inverter. Overall it was like taking a blanket off the speakers and made the harmonics come to life without all the compression.

 

I then started shopping power tubes. I had a gift card and bought a set of Ruby Tubes. Bad mistake man. Ruby sorts and matches tubes from a China manufacturer and brands them with their name.

I had them in there running for 30 seconds and hear pops and crackles while setting the bias. Then I heard a loud pop and shut the amp down. I pulled those crapper out and sent them back to MF for a refund.

 

I ran the Groove tubes again for a few months. There was nothing wrong with them. They'd likely still be running for several more years but just due to age an mileage I wanted them swapped out.

 

The next set I tried were JJ's. I had good luck with the JJ EL34's so I figured I'd give them a shot. Their specs are good and have decent prices.

Put them in, set the bias and there in the background I was hearing a little crackle and popping. Not nearly as bad as the Ruby's but enough to know I wasn't going to be running them. I should have tried them out right away then sent them back but I procrastinated for several months and didn't think it was right to send the tubes back at that point. I ran them for maybe an hour or two at most.

 

Next I bought a set of Electro Harmonix power tubes. Holy cow did that make a difference. They are built like the old RCA tubes the Fenders used to use and the head really sounds good now. Between that and the caps both channels smoke for tone now. Even sounds good playing bass through it too.

 

I got a gig this weekend so I'll likely take this one out for a spin. Its a really loud 50W amp though. I'll probably use my small 2X10 cab with it. My 4X12 2X12 and 4X10 cabs will be much too loud. What I really need to do is build a single speaker cab for it which will sound good yet not be overly loud. The head sound excellent when cranked to about 5 where you start getting that juicy compressed tone. Most of the speakers I have starts peeling the paint off walls at 3.5 on the volume.

 

Most of my spare 12's are those old black magnet eminence speakers. They sound fantastic with that amp cranked I'm not sure what they're wattage is. I cooked one before with that Bassman head running at 4. They sounded fantastic like a tube head should giving me those ZZ Top tones for about 10 minutes then it just fizzled out and died.

 

They are old but I thought the speakers could handle 50W or more just based on the magnet size. I suppose I guessed wrong. I want a small cab that will just fit the head neatly with a single speaker. I do have a 70W Jensen mod but I'm not impressed with its treble or bass response. It lacks the edge up top and has too much low end roll off. I have a pair of Weber speakers and that suck raw eggs. Garbage speakers if you ask me. Of course they aren't their top models but even the cheap Jensen mods sound twice as good.

 

I suppose I'll have to start trolling around for something. I do have two 8" peaveys which I could use in a cab. I think they're 25W each but I'll have to double check. I been using them as subs in boxes for my recording setup but changing those over to some other 10's I have wouldn't be too hard.

 

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Well I fixed that problem. Found a bran new 12" 60W Peavey Viper speaker for $35 on bay with free shipping. Not sure if its a speaker peavey makes or whether its just a branded speaker but its got the looks like a decent speaker pulled from a Viper 2 amp. I'll build a light weight cab that I can easily pop in the back of my Mustang and I'm good to go.

 

You can do allot to change a speakers tone by the build of the cab too. Guitar amps don't need to have strict dimensions like a bass cab does so the speaker has matching resonance to the air space. I in fact had to retune my 2X12 cab when I put those Weber speakers in it because there was way too much bass response. I added extra layers of compressed foam in the cab to reduce the air volume and it does a good job cutting down the bass response.

 

I did this one my 4X10" cabs too. They were originally closed backed cabs and I cut them partially open in the back and they sound fantastic now.

Considering the peavey speaker is designed for an open backed cab and knowing the head's response I'll stick the speaker in the 2X12 cab first so I know what it can produce for tone. Then I'll know what I need to do for it. I'd like to use a larger baffle made of thin plywood and suspend it on two sides like they used on some old fender amps. The thin baffle vibrates to give some extra woody sound. I need to look up some specs and see how they used to make those cabs. I have some ideas but I wouldn't want it to vibrate and make noise.

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