Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jordan86 on November 18, 2020, 08:37:16 pm
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There is a ‘65 Showman head for sale locally by me for only $650. It’s actually a dual showman, or at least it has the 4 ohm dual showman OT. It seems to be real clean and everything is original, including the blue caps. A few filter caps in the doghouse have been swapped but that’s it. Will need all new caps but I’m sort of wondering if I dip my toe into a restoration project.
1) $650 seems like a good deal, no?
2) with the 4 ohm OT, I could hypothetically pull two 6L6’s and run at 8 ohms instead of 4? I don’t need 100watts :)
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I'm not very good at guessing values on vintage tube amps, but it seems like it's probably a reasonable price if it's in good condition cosmetically and it works.
As for pulling two of the 6L6s to run it in 8 homes, a friend of mine had a late 60s silverface Dual Showman Reverb amp, and that's what he did to use it with an 8 ohm cabinet. He still could only play it on about 3-4 on the volume without it getting way too loud in the bars where we were playing at the time. :-)
If you get the amp and want to do the thing with an 8 ohm load, pull either the 2 outer 6L6s or the 2 inner ones. That is 1 from each side of the push pull transformer with normal Fender wiring. Of course, if you pull the chassis to replace any capacitors, you can verify the power tube wiring to the OT so that you get 1 tube from either side instead of both tubes from one side of the OT.
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Showman head
IMO, it is one of the lowest price I see sometimes if ap is in top shape.
https://www.creamcitymusic.com/vintage-1966-blackface-fender-showman-85w-tube-amp-head/
Average price from Reverb.com is $1000
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1) depends on the cosmetic condition & if the transformers are original and working, $650 is a fair price. check the serial no. for build date confirmation - someone could have replaced the faceplate on a 70's silverface. if it's a 100W model, it should have the DUAL showman faceplate. perhaps it was converted to 100W sometime in the past when replacement DUAL showman OT were available, but that would require a PT swap as well.
2) yes, you can pull 2 tubes - be sure it's one from each phase not both from a phase. yes, you'd double the load Z to compensate.
would be cool to get the 2 x 15 cabinet loaded with the JBL D130F as well - the dick dale memorial combo. if you do get it, you're probably going to fall in love with the vibrato, if not already a fan.
--pete
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Here it is. Good cosmetic condition. Chassis stamp coincides with late 1965. The transformers appear original.
https://denver.craigslist.org/msg/d/denver-fender-showman-amp-head-1965/7233052896.html
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Here it is. Good cosmetic condition. Chassis stamp coincides with late 1965. The transformers appear original.
https://denver.craigslist.org/msg/d/denver-fender-showman-amp-head-1965/7233052896.html
Transformers: 1965, 32th week, 14th week and 39th week
Original,* nice and clean amp.
* except 2 filter caps , you need to replace all other and bias caps.
I'll replace all bypass caps too ( 25 mfd 25 volts )
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Its about the average per reverb.com's price guide. Probably worth it.
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Looks good to me. I'd replace all the electrolytic capacitors if I bought it and intended to play it. Sure there is one newer PS filter cap but I'd just replace with 5 brand new F&T caps. Throw the orange one in the middle in the used parts drawer. Id also replace the rectifier diodes with 4 1N5408s. I'd also update the AC input wiring to the current NEC standards
Nice find. :icon_biggrin:
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Thanks all. I messaged the seller. I would definitely plan to replace all the filter caps with some nice F&T's, as well as the bypass caps.
Do the prestigious blue molded caps have the same "shelf life" as electrolytic caps? I'd love to keep those for originality sake if I could. It would be a restoration project though, with the purpose of getting it to playable and schematic spec. I presume they would need to be tested for their capacitance and ESR values. I've watched a good bit of Uncle Doug so I should be able to manage that as well :)
The death cap and 2 prong power chord would definitely have to go as well.
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I did a repair job earlier this year on a super reverb, NO way I change ANYTHING that wasn't broke. I highly recommended a 3 pronger, the owner just smiled n said it was worth more as a 2 prong. replied, as long as you live to sell it :icon_biggrin:
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Thanks all. I messaged the seller. Will hopefully be picking it up this weekend.
One thing I noticed in the schematic is that there is no CT on the heaters. No artificial CT either off the pilot light. The schematic shows a grounded center tap and says “internally grounded”. Does that mean there is an actual CT inside the transformer?
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The schematic shows a grounded center tap and says “internally grounded”. Does that mean there is an actual CT inside the transformer?
yes
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I know this is an opinion question...but how strongly do you guys try to keep everything stock? Let's say 20% of the caps in the amp are either failed or far enough out of spec to be considered "failed". Do you...
1) Live with it and just make the most of it.
2) Replace just those few and keep other stuff stock.
3) Replace all the caps for consistency of look and function. Store stock components.
Seems to me 1 and 3 are the only practical options. If you start replacing ANYTHING, you may as well get EVERYTHING up to spec.
I'm open to wiser perspectives though!!!!
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the amp in that craigslist link does not have pitch shift vibrato and it seems that it does have tremelo instead. the clue is that it has only 4 preamp tubes. i presume then that the 6G14/6G14-A models are the most desirable models?
--pete
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replace ALL the electrolytic caps. test the coupling caps and ceramic disc caps & replace caps that have excessive leakage. replace resistors that have drifted out of spec by more than 10%.
keep as much of it stock as possible. why would you leave failed parts in service? that makes no sense unless you just want to have a museum piece. leaving parts that are out of spec installed anb the amp probably won't sound as intended when new.
--pete
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Got the Showman. Put in a grounded power chord and fired her up. What a sound!
Voltages check out within 10-20 volts. Most the resistors are at least 5% out but all are within 10%. Checked the 6L6 bias. Most of the power tubes were in the ballpark of 60ma!!! Got it dialed closer to 35ma now. Amp is actually noisier now than before. I think tubes are poorly matched. I noticed swapping placement during bias created more hum. Will continue to experiment.
Still trying to figure out how to measure caps without removing them. Is that even possible? Struggled with my Fluke 87 meter.
Only quirk is 400+ volts on one of the vibrato circuit triodes. I think some caps are going. Will post a clip with schematic and voltages on another thread.
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Only quirk is 400+ volts on one of the vibrato circuit triodes.
That's normal if you don't have a footswitch or the footswitch is turned off.
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Only quirk is 400+ volts on one of the vibrato circuit triodes.
That's normal if you don't have a footswitch or the footswitch is turned off.
The voice of wisdom speaks. Thanks, Sluckey! I do have a foot switch but it was not plugged in when testing voltages. Good to know.
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Just playing around with the Vibrato channel on my Showman and noticed it basically stays clean to 10. Not sure if this is typical. I assume it may be since I've read many of the other 2 stage blackface amps stay clean all the way up the dial. Also, I understand that the load from the vibrato circuit sort of knocks back the drive on that channel as well. The normal channel starts to break up around 6 or 7 on the volume dial.
Just curious if any other Showman users out here have the same findings. I did notice my plate voltage on the second stage of the Vibrato channel is only 265v (should be 280v). All the others measure at spec. No significant resistor differences on the rest of the circuit.
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congratulations on the Showman! I've got a 6G14A model, and have a number of friends with the AB763 version. (these things happen when you play surf music!)
Anyway, they don't particularly break up, though the sound gets a bit of hair once you've got the volume up north of 12 o clock.
You're correct, the tremolo circuit takes a bit of volume off that channel, but in return you get tremolo, so in my book, it's worth it. Also, since there's no reverb, the two channels are in phase and you can get more breakup by using both channels jumpered together.
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Very cool. Yes I love jumpering the channels. Normal is fat and full. I pull back the mids on the VIB channel so it’s bright and open and chimey. Together is a wall of clean goodness. It does start to break up with both channels pushing together. As for the volume discrepancy...
The normal channel on 4 is about as loud as the VIB on 7. Quite a big difference. As to the plate voltage differences on V2, I’m wondering if the tube could be causing that. I’ll try swapping V1 and V2 to see if there’s any noticeable changes.
Other than that, it may need new plate load resistors. After replacing the electrolytics the amp is a good bit hissy. Liveable though.
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That much volume difference between channels doesn't seem right. I'm by no means an electronics expert, but it's possible the opto-resistor bug is passing signal to ground when it shouldn't be? The other possibility, incredibly stupid, but possible, is that the volume pot on the vibrato channel is either dirty or simply bad. Over the years I've had to spray contact cleaner on my Showman's volume pot for crackles and the like.
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The big difference in volume is due to the 50K INTENSITY pot that drags the VIB channel signal down. A popular mod is to switch the INT pot out of the circuit. That creates a BIG BOOST, probably making the VIB channel about equal to the NOR channel.
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Thanks all. I swapped V1 and V2 and the difference between the two channels lessened. They are OOOOLD GE valves, so I think they are just a little worn out.