Members Chris Loeffler Posted January 11, 2017 Members Share Posted January 11, 2017 My CL ad asking local musicians what sort of old gear they had around that they were interested in swapping for yielded another interesting find... a Musicman HD-130 tube head! Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 11, 2017 Author Members Share Posted January 11, 2017 Front shot... pretty good condition for the age. Supposedly a single-owner amp. Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 11, 2017 Author Members Share Posted January 11, 2017 Back shot... I'll take it apart this evening to look inside. Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 11, 2017 Author Members Share Posted January 11, 2017 I know there were a few variations on this theme, so here's what I have so far- The Musicman HD-130 was supposedly meant to be Leo Fender's Twin Reverb killer, with a massive power section, a single 12ax7 phase inverter/driver, and a solid state preamp. These were originally equipped with 6CA7 tubes, which I understand to be American production EL34s. Although the person I got it from was pretty sure it was tubed with the same style tubes as the original, there are clearly GT EL34s in it. I'm finding conflicting stories about what an appropriate analog is in a current production tube (if there even is one). Seems there's a fair amount of argument as to which tube type is the best replacement, especially given the high voltages hitting the plates. Link to comment Share on other sites More sharing options...
Members Mr.Grumpy Posted January 11, 2017 Members Share Posted January 11, 2017 The "HI/LO" power switch in fact selects the B+ (plate) voltage for the power tubes. So if you can resist the urge to run it "HI" power, you don't get the crazy-high B+ voltages on the tubes' plates. I have an HD-212 combo, with the later "One-Fifty" (as in WATTS) version of this amp that doesn't have the phase inverter tube. On LO power, the B+ voltage is about 480 volts as I recall, on HI power the B+ is over 700 volts! So if you can keep it on 'LO' power, any old EL34 tubes should be OK. As you're probably aware, these amps are really, really clean sounding. I haven't run my Music Man at HI power in years, except to test it. A 2x12 combo with 75 watts is plenty loud for my needs. In any case, the One-Fiftys use plain old 6L6GC power tubes and don't have the phase inverter tube. The amp design is a bit unusual, but schematics are available on the web, so keeping it going shouldn't be a problem. OH, I just saw that this is the BASS version. Bass players LOVE these. Yeah, find the right tubes that will handle the high plate voltages if you're going to use it for bass. Happy New Amp day, sir! Link to comment Share on other sites More sharing options...
Members DeepEnd Posted January 11, 2017 Members Share Posted January 11, 2017 Congratulations and Happy New (Old) Amp Day. Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 11, 2017 Author Members Share Posted January 11, 2017 As you're probably aware, these amps are really, really clean sounding. It's my "anti-Magnatone" acquisition :-) Link to comment Share on other sites More sharing options...
Members WRGKMC Posted January 11, 2017 Members Share Posted January 11, 2017 I have a 65W version in mint condition. Not a single scuff or rust on it. My buddy was moving out of state and sold it to mein non working condition for $50. It only had a couple of cracked solder joints and it back up and running. Its a late 70's versionthat had the inverter tube. They're selling for around $800 these days. I eventually bought a pair of 6CA7 tubes which are the original tubes the amps were designed for. They are not the same as EL34's. It’s The 6CA7 has more headroom than an EL34 and by the time you get it really crunchy sounding your pants are flapping in the breeze. They can take the super high plate voltages the amps have better then EL34's can. Electro Harmonix has reissues them and it gave the head a warmer tone then the JJ EL34's that were in there. You have to re-bias the amp for the tube change. JJ is making 6CA7's too. The JJ 6CA7 tube looks and sounds like a 6L6 but biases like an EL34. I hear they have a little better bottom and mids then the EH have. I haven't tried them yet however. I have low hours on the EH so it will be awhile before I try those. If you do plan on changing the tubes or re-biasing PM me. There's an unofficial music man site out there that has the biasing procedures but its got some bogus information. I had to dig long and hard through those forums before coming across the right info. There was a decimal place error which made the readings off by 10X and the readings for EL34's aren't the same as the 6CA7's. Overall the 65W version is more then enough power for my needs. The 130 would be ungodly loud even in the low bias mode. I'm not a big fan of the low bias modes either. The tone gets dull and farty sounding. If I need lower volume I simply use less efficient speakers. Tone wise I'm not overly thrilled with the Music Man. The SS front end isn't that impressive sounding but at least the tubes help quite a bot. The overdriven preamp sound is pretty dated too. Not allot of usable tones there but using the amp clean with pedals is pretty good. I can say My Vintage Bassman does have better tone when you run the two side by side. Still it's kind of unique. The Vibrato is very cool and unique sounding. it doubles in variance when you pass the half way mark. The reverb is quite different then fenders too. Its tone has more upper mids and is less scooped. Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 12, 2017 Author Members Share Posted January 12, 2017 I eventually bought a pair of 6CA7 tubes which are the original tubes the amps were designed for. They are not the same as EL34's. It’s The 6CA7 has more headroom than an EL34 and by the time you get it really crunchy sounding your pants are flapping in the breeze. They can take the super high plate voltages the amps have better then EL34's can. Electro Harmonix has reissues them and it gave the head a warmer tone then the JJ EL34's that were in there. You have to re-bias the amp for the tube change. JJ is making 6CA7's too. The JJ 6CA7 tube looks and sounds like a 6L6 but biases like an EL34. I hear they have a little better bottom and mids then the EH have. I haven't tried them yet however. I have low hours on the EH so it will be awhile before I try those. If you do plan on changing the tubes or re-biasing PM me. There's an unofficial music man site out there that has the biasing procedures but its got some bogus information. I had to dig long and hard through those forums before coming across the right info. There was a decimal place error which made the readings off by 10X and the readings for EL34's aren't the same as the 6CA7's. Overall the 65W version is more then enough power for my needs. The 130 would be ungodly loud even in the low bias mode Yeah... I'm thinking I'd like to get this back to original specs. Time to price out the two tube options! I will holler once I get them. Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 12, 2017 Author Members Share Posted January 12, 2017 Tone wise I'm not overly thrilled with the Music Man. The SS front end isn't that impressive sounding but at least the tubes help quite a bot. The overdriven preamp sound is pretty dated too. Not allot of usable tones there but using the amp clean with pedals is pretty good. I can say My Vintage Bassman does have better tone when you run the two side by side. Still it's kind of unique. The Vibrato is very cool and unique sounding. it doubles in variance when you pass the half way mark. The reverb is quite different then fenders too. Its tone has more upper mids and is less scooped. I got it to put "amp in a box" style pedals in front of and run the preamp clean, so it sounds like a good platform, based on your assessment. I have a visual sound workhorse I picked up on the super cheap and it just doesn't sound right. I'd love for this to fit that application. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted January 12, 2017 Members Share Posted January 12, 2017 The speaker choice may be a big factor on the heads tone. I've always liked the tones Johnny Winter got from his 4X10 combos but I haven't been able to nail those tones with a head and cab. The amps were usually paired with Fane Speakers which I suspect give the head its unique tone. Cab size of course affects the bass resonance. I've used the head with Eminance 12's and Jensen Alnico 10's mostly. I usually run it on my open backed 4X10 cab with the Jensens and its a bit bright with those speakers. I have to dial the mids and treble back quite a bit. The Fender sounds great on that cab but the Music Man like I said is a bit bland. I guess I should try it on my Marshall 1960 can with 4 Celestion cream back 75's. I suspect it would sound allot better on that cab. I tried it on a 2X12 with a pair of Webber speakers and it croaked badly. Those speakers aren't that hot so I didn't expect much. The Peavey 4X12 sounded OK with its unbranded black magnet Eminance speakers commonly used in those older cabs. I have a bunch of others but really haven't experimented with them and that head. I know what the head does and can predict the outcome with them. The best match I've found was running the head on an old Traynor Bass cab that has two 300W Celestion 15's. I had the cab laying around and bought a pair of 15's on sale. Apparently Celestion was making some branded speakers for Trace Elliot and I found them on sale new for $50 each so I grabbed a pair. The Traynor cab is more shallow then a Bassman 2X12 cab (used to own one) and not much good for bass tones unless you have the original speakers. I suspect the original speakers had a response curve that sounded good in that shallow cab. The cab sounds fantastic for guitar which wasn't my intention but just happened to work out that way. Link to comment Share on other sites More sharing options...
Members Chris Loeffler Posted January 12, 2017 Author Members Share Posted January 12, 2017 http://www.eurotubes.com/store/pc/viewCategories.asp?idCategory=63 Ordered. Will report back after a re-tube and bias. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted January 12, 2017 Members Share Posted January 12, 2017 Found this for you. Section II GRID BIAS CALIBRATION (This applies to all models "using 12AX7 DRIVER TUBE") A. This applies to all models using a grid drive. (12AX7 driver tube). B. Adjustment is as follows: 1. Turn the amplifier to "on" with the HI/LO Switch in the HI position. No signal. 2. Using a volt meter, measure the voltage from cathode (pin 8) to ground on the output tubes. Across the 10 OHM cathode resistor is a convenient measuring point. 3. Adjust the bias trimpot located farthest to the right (looking from the front) on the GB-1 and BB-1 circuit boards until you read .5 volts DC across the 10 OHM cathode resistor. NOTE: Be sure tubes are warmed up before adjusting the bias voltage. If you want you can dig through these forums to find more info. http://www.pacair.com/cgi-bin/discus....cgi?pg=topics Here's the original Bias and tremolo adjustments. I believe your amp has the inverter tube so the procedure is the second one. The first is for amps that have a SS Inverter. http://www.pacair.com/mmamps/Documen...letin%201m.pdf Now there was some discussion in the forums about some amps having 100 ohm cathode resistors. It changes your voltage readings by a factor of 10. I Think I was reading 5V not .5 volts when I want from EL34's to the 6CA7. I can't be too sure its been a couple of years now. I do remember It was different then what was posted in those original bias instructions which had me mystified. I kept digging through those forum threads and eventually came across someone mentioning the resistor differences on different amp versions. You cant adjust the bias from .5v up to 5V or vice versa so its not going to matter. Whichever resistors you have you set it to 5 or .5v. I also believe you can tweak the setting hotter or cooler with no problems. I heard no notable difference in tone with the bias hotter or cooler so I simply played it safe and went for the factory settings. This will give me maximum tube life and avoid any long term issues where the tubes may cook and red plate. (red plating is sneaky and mis-biased tubes cant take awhile before exhibiting issues. I suspect your amp has two bias trim pots, one for each set of tubes (likely 1 & 3 - 2 & 4) I suspect that simply used two of the 65 boards on the 130W model so the bias procedure is the same for a quad set X 2 Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted January 13, 2017 Share Posted January 13, 2017 Congrats on the new amp Chris. Those JJs should be a good choice for it. Link to comment Share on other sites More sharing options...
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