Name: Dan H E-Mail: ********** Date: 12/16/99 2:05 AM Subject: Re: Recommended mods to AB165 Bassman William, Check out my post at harmonycentral.com "amp review" "Bassman 50". I converted mine to AA864 specs, left the normal channel alone, but redid the Bass channel w/same caps/tone stack as '59 Bassman/JTM45! (Modding an old amp to sound like an old amp then modding it to sound older?). The post shows how to hook up to the 2nd 12ax7 (remove interstage resistor, V1 to .02 cap to 220k w/250pf across it, input of v2 run a 15k to ground). Mods on V2 are critical to get a little of that "post eq" sound on a "pre eq" setup. I have a JTM45 RI & the mod makes it close (not identical). Makes even G12T-75's sound great! I run the same kind of stompbox/single coil rig, the whole deal sounds a bit "Cream". Dan Hostak * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Price Paid: US $150 Features: 7 This is an addition to my previous comments listed below, hope it eliminates any confusion. Dan H. Sound Quality: 9 Before you mod the 2nd 12AX7 there is an interstage 470k (or 220k) resistor that must be removed. It's located off the yellow wire from pin 6. The other end of the resistor is at the junction of another 220k resistor and a .01 cap. Remove it. Now, starting at pin 6 of 1st 12AX7 is a 220k resistor, replace it w/a .02 cap. Next in line is the .01 cap, replace it w/a 220k resistor (which then goes to pin 7 of the 2nd 12AX7). At this point run a 15k resistor to ground. Now follow my previous comments on the 25uf bypass cap. To install a "middle" control all you are doing is replacing the 8.2k resistor (or the 6.8k on the "normal" channel) with a 25k or 10k 1/2 watt pot. Check out Gerald Webers book "A Desk Ref. of Hip Tube Amps" or the Groove Tubes book and look up a Fender Twin schematic to see how to wire to pot. Also, when modding the power amp to AA864 specs. make sure you do the bias pot conversion. Step by step instructions are in the Weber book. Reliability: 10 See prev. comments. Customer Support: 10 Forgot to mention the Groove Tubes book. Compare the schematic of your silverface to to AA864 and my mods before beginning any work. If you are not sure, have a good tech show you! The world needs as many guitar players as possible, you can get killed if you don't know what you are doing!! Overall Rating: 9 One more tip about cabs. Ken Fischer (Trainwreck Amps) suggests using 20' of 18 or 20 guage speaker wire. Thick, short wire is good for bass, but long lengths of thinner wire give more chime & jangle. Try it, it works! Also, Bassman heads are 4 ohms, so a 4 ohm cab will give you a cleaner sound, an 8 ohm cab will distort a little sooner. Check out Carvin, they now have two cool 4 ohm ext. cabs, for low buck$$. Submitted by Dan H. in Hopatcong NJ at 04/17/1999 10:14 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Price Paid: US $150 used + $75 parts + 6 hrs. time Features: 7 Great sound, so easy to operate you can focus on your playing and not your amp! Since I agree w/previous comments maybe someone can benefit from my mods. I'm a "roots" strat player. I converted my silverface to blackface (BF) specs. Normal channel is "spanky" clean BF for rythym & country licks. Bass channel conversion sounds like a mix between BF fender & JTM45 for lead work. A tube screamer shines here! Sound Quality: 9 On some silverfaces there is an extra 8 or 16uf filter cap that causes a stiff, brittle guitar tone. Follow the AA864 schematic & lose it! Change phase inverter 12AT7 & 6L6 wiring along w/feedback loop to AA864 specs (don't forget to swap the output transformer green & black leads!). BASS CHANNEL: convert tone stack to "59 bassman/JTM45" specs-250pf silver mica, & 2).02 caps w/a 56k slope resistor (some of you guys using a Marshall 4x10 might like a .1 cap to treble & bass pot instead of a .02). Rewire the "deep" switch w/a 100pf silver mica cap. Check out the "normal" brite" switch to see how it's done. Off pin 6 of 1st 12AX7 where it meets 100k plate load resistor install .02 cap followed by 220k resistor, which then goes to pin 7 of 2nd 12AX7. At this point run a 15k resistor to ground. If you want more gain & crunch try 20k to 100k! Off pin 8 of same tube lose the 25uf bypass cap, but leave the 1.5k resistor in place. I drilled a hole next to the normal bass control and installed a 25k "middle" pot f/the bass channel-on a silverface if you do this right it doesn't look out of place. if you can find a dual 25k or 10k pot-Voila! you can have a shared mid control (something you guys wished the amp had!). Remove any 500pf or .01uf ceramic caps in parallel w/100k resistors. For new caps I used sprague "orange drop" 600v. Reliability: 10 When I got this top some fool wrapped aluminum foil around the fuse which was blowing due to a shorted 6L6. This caused a fire in the amp & burned up the 6.3v heater wires to the transformer! Spliced in new wire, new fuse & 6L6's (biased to 28ma), & the head worked great! How many other amps work great with minor repairs after a FIRE? Customer Support: 10 I recommend www.hoffmanamps.com & www.angela.com f/tubes & parts. Also get Greald Webers & Dan Torres books (available from J K Lutherie email: guitar@jklutherie.com). I got my ideas & learned how to do basic repairs from these books. Overall Rating: 9 For open back cabs try Sovtek 5881's f/closed back I like the Sovtek 6L6WXT. I tried my best buddy's (AL) Vibroking 2x12 cab & it sounded real cool although I prefer the Marshall 1922, 1936 2x12's. For small gigs I use 1912 1x12 (open back conversion) w/a G12T-75 Celestion. I give this a "9" since my JTM45 reissue is a "10". But the 1972 Bassman Head is my workhorse! Hope this helps do-it-yourself cheapskates like me! Submitted by Dan H. in Hopatcong NJ at 04/16/1999 07:30 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Steve, Thanks f/your compliments! Posting the info is fine w/me but pls. do delete my E-mail address (Too much time tweaking amps, BBS reading, not enough time playing!). BTW some minor notes: I now have the 100pf mica cap wired directly across the volume pot, hooked the 250pf ( in series w/220k resistor) to the "deep"/brite switch w/a 10 meg resistor across it to prevent "popping" when switching. In the down position (series cap out) it's better f/closed back cabs & with a open back cab w/a TS9/Strat combination you get the Clapton "built in boost" thru tweed twin sound. (unwound strings really sing when bent). In the up position you get glassy clean & brittle crunch sounds. I also put in the New Sensor 2,4,8 OT, one jack is 8 ohm w/NFB & the other is 4 ohm. I use 8 ohm cabs & sometimes I need the headroom of proper match, yet the mismatch (using 4 ohms) does mimic the mismatch of the JTM45 RI OT which I love. (16 ohm has NFB yet I'm using the 8 ohm jack, similar relationship). I need to keep the 25k mid pot because at "3" on vol. f/most club/top 40 gigs w/TS9,DDL & chorus the mids also need to be at "3". Opps! I forgot we're into vintage! With vol. on "7" and the mids (25k) on "10" you get a outrageous natural overdrive. (Guitar/cord/amp, of course). One other slight change is the PI input cap from 500PF to .001 orange drop. Also did the new Gerald Weber deal where you mount the tone stack directly to the pots and eliminate excess wire (All these bass channel mods add gain/noise). Excess hiss was driving me nuts so I changed the new 100k plate load resistors from new carbon comp to metal film, really lowered the noise floor (all other resistor in signal path are carbon comp) & didn't affect tone. I appreciate your comments on rewiring PI however I was determined to keep that stock AA864 because I wanted the normal channel pure (though I did add a .047 cap before the 220k mix/blend resistor ala Bandmaster. So, a head (which may wind up in a Rodgers custom combo pine cab) I got f/ the spanky country normal tone spends more time as a blues/rock machine! Too much fun, and $150 + OT & parts, etc.! If any of these updates/rambling have merit feel free to post them as well, & thanks so much! Dan H.