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Post subject: Bassman 10 silver 70w 4x10 with JBL k110's question/HELP?
Posted: Sun Oct 10, 2010 1:02 pm
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I have recently been given a Bassman 10 70Watt 4x10 combo, G.E. 12AX-7's and AT7 (no 6L6's),
FRONT: BASSMAN 10 (fender music company) silverface
Channel 1 Bass PRE, LOW, MID, HIGH, and the "normal channel" PRE, LOW, MID, HIGH.>>>>>>>>.MASTER VOLUME...red lamp
REAR: "hum" ">>>MAster tube output pot">>>EXTENSION speaker jack,>>> Main speaker jack states(minimum 4 ohm load) >>>>standby, power toggles,

SPEAKERS: 4x10 JBL K110's (one not working) and one has a pin hole in cone.... the remaining sound fine

Tubes: GE 12 ax7a, GE 12ax7, GE AT7, V1 is loud to the tap but doesnt appear to be microphonic.

serial is torn....maybe 3 letters/numbers left.

This combo was in horrible condition cosmetically when given to me. I'd like to think that I "rescued "it from further disrespect....mold, mildew, 90percent of vinyl gone, mouse chewed speaker cone leads....

SInce, ive sanded, re finished and cleaned the chassis/cab...I'm using 2 mesa 6L6's I had to spare with the GE's it came with......

I wired 2 of the 4 speakers 8ohm so as of now it's running 2x12 (with the other 2 remaining false in cab)

Up and running with some burn time, this amp sounds pretty sweet!

Questions:

1. can this amp be harmed without biasing the new 6L6? (sorry i play mostly mesa which do not require mismatch/load issues) Can you offer a link so i can possibly bias this amp myself?

2.how can i determine the year?

3. is "jumping channels bad for this unit?( I am VERY new to Fender)

4. I have a wide selection of MESA, J/J tesla,ARBI, AX7-A, AX7, SPAX7....any tips, suggestions,preference for pre amp tubes? leave the OG's in?

5. Is running only 2 JBL's harmful to this unit or the speakers at this wattage (70w)? Are these speakers sought after? Ive only read the review on harmony central...

6. will runiing the Extension cab (maybe a 15 or 12) at 8 ohms with the native speaker 2x12 at 8 ohms be a safe load for this amp? it states " a min of 4 ohm load"

This has been such a great project to work on! of course I'd like to keep it as original as possible, but I DO NOT want to spend money on this amp at this time. I'd like to use what resources I already have here if possible. thanks for any replies in advance. I would really like to incorporate this amp in my rig. ANY tips suggestions and long rants are welcome! I have been doing as much research as possible online but would like to hear from recent users of the Bassman 10's cheers


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Posted: Sun Oct 10, 2010 2:56 pm
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Joined: Fri Feb 05, 2010 4:31 am
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Location: Province de Québec, Canada
for dating, look the post after yours : Fender twin reverb age


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Posted: Sun Oct 10, 2010 11:10 pm
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Cool amp, T ! Not biasing the tubes shouldn't hurt the amp, just the tubes and their associates are affected. As long as they aren't glowing that beautiful red-orange, they're probably OK. Schematic Heaven's site is down for now, so if I can find another schematic site, I'll get back to you on the bias situation. You can't hurt anything by jumpering the channels(w/o schem-don't know about phase cancellation). Arjay would know about the wattage capabilities and value of those speakers. But running the two speakers at 8ohms and adding another 8ohm cab in parallel, is fine. Just found a disc with the schem, let's see if I can get it to work ? Art

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Posted: Sun Oct 10, 2010 11:25 pm
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Joined: Sun Oct 10, 2010 12:20 pm
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thanks for the replies! no odd glow from the tubes, thanks. Yes I am def interested in hearing all about this amp. it is my first tube fender and it now wont be my last after falling in love with the unique tones and versatility (compared to my other vintage tube mesa and marshall rigs). Any other input, good or bad, opinions, or rigging suggesrions (ABY switching, recorsing out jack, amp jumping tricks, and extension cab prefs in combo w 2x10's ...)
I have read the other bassman threads here but im curious about this specific model/ year bassman 10 4x10 combo.... thanks again!


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Posted: Sun Oct 10, 2010 11:30 pm
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Ahh bummer, I 'm no good with computers ! The last time I used this disc, I took it to work and the secretary helped me. Oh well. Art

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Posted: Sun Oct 10, 2010 11:50 pm
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Thanks for the kind intro, Art.

Well, let's see what we have here.

First off, the OP's amp is a 70-watt (allegedly) "ultra-linear" version. In practical terms that means it does not have a traditional bias adjustment. These amps all relied on a "balance" pot in tandem with a "hum" control on the rear panel. The pre-amp architecture is identical to the Super Bassman and Bassman 135 -- a 12AX7 for each channel and a 12AT7 phase inverter.

The ultra-linear amps are brutally hard on output tubes. Only the hardiest of 6L6s designed to withstand 490 VDC at the plates should be used. US-built NOS -- especially mil-spec JANs -- are comfortable in this environment while many of the popular current offerings are not.

Likewise, the ultra-linears used an output tranny with multiple secondary taps and self-switching speaker jacks -- thus, they'll safely run any load from 16Ω down to 2Ω. The original speaker array consisted of four 16Ω drivers (usually CTS but Utah, Eminence, and Oxford were also OEM vendors during this time) wired in parallel for a total load of 4Ω.

The JBL K110 has a rated power-handling capacity of 50 watts continuous. And as much as I love the JBL 12's and 15's, I find the ten-inch editions to be some of the most offensive speakers ever made. I had a pair in a '66 Vibrolux Reverb and they were awful -- they sounded like somebody torturing a smoke detector with an icepick.

That said, in the Bassman 10 with a sealed-back cab they're likely to sound much more pleasing with some rear damping to attenuate a substantial amount of the highs. I would check each speaker with a DVM to ascertain the actual impedance since most JBLs have been re-coned and kits for all common impedances are routinely available.

The chassis shares its dimensions with the ultra-linear Super Reverbs, Pro Reverbs, and Bandmaster Reverbs of the era -- if conversion to a piggyback configuration is contemplated, Mojotone and other aftermarket cabinet builders offer off-the-shelf products suitable for this purpose.

Best of luck, HTH

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