Fender Bassman 70

[mikechenko]

Hey everybody, new to the forum and still fairly new to playing bass. Over the weekend, my wifes uncle had given me a 1970's Fender Bassman 70, I have a 1990's 500 Watt Carvin, 15 inch cabinet. Any help on what kind of sound I'm going to get out of it? Proper speaker cable to use? I don't gig, mainly play around the house and with friends at our practice space. Since I've only had a 15 watt practice amp I've been playing out of, It'll be nice to set everything up. Both cabinet and head were given to me for free, if I have a bunch of junk on my hands, I'm not going to be terribly upset, since I didnt waste money on it. Any help, suggestions, advice would be greatly appreciated.

[fuzzy beard]

Official Fender Bassman club


Also did he tell you the last time it was used or serviced? Tube amps are different from solid state. And need service from time to time.

[fuzzy beard]

Also that is far from junk!!

[mikechenko]

It does work, and I am aware of the differences. He had said that everything was in working order. I do know that I dont have junk on my hands, just not sure on how cabinets and heads work together, with the differend wattage and Ohms and whatnot. Should have stated it differently.

[fuzzy beard]

Is it a bassman cab? Any way to get pics?

[mikechenko]

Carvin cab, 1x15 inch 500 Watt. I can post pics tomorrow.

[fuzzy beard]

You know what ohms that is? should say on the jack plate.

[mikechenko]

8

[fuzzy beard]

Year:
1968-1983
Model:
Bassman (68-71)
Bassman 50 (72-76)
Bassman 70 (77-83)
Circuit:
AB165, AA568, AA270, AA371
Config:
Piggy-back
Control Panel:
Silver forward facing w/ blue labels
Front Conrol Layout:
Bass: In, In, Deep Sw, Vol, Treb, Bass - Normal: In, In, Bright Sw, Vol, Treb, Bass - Pilot Lamp
Rear Conrol Layout:
AC Outlet, Ground Sw, Fuse (2A), Power Sw, Standby Sw, Speaker Jack, Ex. Speaker Jack
Knobs:
Black skirted w/ chrome center, numbered 1 - 10
Head:
8¼" x 22" x 9½" (21 x 55.9 x 24.1 cm)
Head Hardware:
Black strap handle, 4½" chassis straps, corner protectors, cab hooks (68-76)
Cabinet:
68-71: 40" x 29½" x 11½" (101.6 x 74.9 x 29.2 cm)
72-83: 30" x 28" x 12" (76.2 x 71.12 x 30.5 cm)
Cab Hardware:
3 Black strap handles, corner protectors, knurled studs (68-76), casters
Head/Cab Covering:
Black Tolex
Head/Cab Grille:
Blue sparkle grille cloth w/ aluminum frame (68-69), w/o aluminum frame (70-79)
Logo:
Grille mounted, raised, chrome & black script "Fender" w/ tail(68-74) or "Fender®" w/o tail (74-83) (head and cab)
Weight:
105 lbs. (47.6 Kg)
Speakers/Load:
2 x 12" (68) or 2 x 15" (68-83)/4 ohms (8 ohms each in parallel)
Speaker Model:
Oxford 12T6, Utah or Rola
Effects:
None
Output:
50 (68-76) or 70 (77-83) Watts
Preamp:
Bass: 2 x 7025
Normal: 7025
Power:
2 x 6L6GC
Bias:
Fixed Bias, ajustment pot
Rectifier:
Solid State
Phase Inverter:
12AT7 (long tailed)
Comments:
Fender switched back to the blackface era cosmetics some time in 1980. Bassmans produced between late 1980 and 1983 have a black control panel and silver sparkle grille cloth.

[fuzzy beard]

Yes, the Bassman 70 will drive two cabs.

Yes, the "ext speaker" jack is where you'll connect your second cab.

This is one of those amps that play with output transformer secondary-winding selection depending on whether or not the extension speaker jack is occupied. When only the main speaker is plugged in, the full winding is used. When two speakers are plugged in, only half the winding is used.

Although the schematic doesn't come right out and say it, it seems clear that each jack wants to see 4 ohms, for a combined impedance of 2 ohms. The main jack is denoted 068270 SPKR JACK FOR 4 OHM MIN. LOAD, and the extension jack is denoted 014143 EXT. SPEAKER JACK FOR 4 OHM MIN. LOAD. That and the split secondary winding tell me it's 4 ohms per jack.

What'll happen? According to the schematic, nothing bad, since it says "minimum" load. From that, we can assume there's some safety margin in the output section of that amp.

The above is copied from a reply in a different thread by Craig p.New Cabs for a Bassman 70.

[fuzzy beard]

In my opionen 8ohms will be fine.

[mikechenko]

Originally Posted by fuzzy beard

In my opionen 8ohms will be fine.

8 on the cabinet, correct? Thanks for the info, hope to get this set up within the week.

[mikechenko]

a few pics

[mikechenko]

few more

[Stumbo]

Originally Posted by mikechenko

Proper speaker cable to use?

Any reasonably priced 3 foot speaker cable will be fine. Around $10 bucks or so.

Also, make sure the cab has about 1.5-2" of insulation (open cell foam) on all sides except the baffle (don't block the port if there is one). Oh...if the power cord is 2 prong, get that bad boy switched out to a 3 prong grounded ASAP.

Let us know how it goes.

When you turn on the Bassman, turn it on it stand-by mode for about 5 minutes for the tubes to warm up. Then turn off the stand-by.