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Two Track Music is a somewhat 'laid back' community.  Just some good musicians and song writers hanging out, and having a good time.  We're not a high pressure or fast paced site, we just enjoy kicking back and making some music, and having fun while we're doing it.

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Joom

Today at 02:38:32 PM
I've said for years that it's too bad we're all so far away.  I have made such good friends here over the years, and will never get to even shake their hands...  :(
 

Joom

Today at 02:33:34 PM
Coffee would be great, Ag.  Too bad we're so far away.  Weather is suddenly getting lots better here, snow and ice and those 3ft banks should be melting down soon...
 

agradeleous

Today at 10:03:28 AM
Thanks Red 🙂 I had no idea anyone was listening lol I record more and stop buying guitars , mid life crisis? Lol
Joom I hear ya wish I could drop by for coffee and let ya vent . 😌 hopefully it will end soon .
 

Joom

Yesterday at 06:11:26 PM
Still shoveling, Ag.  These last 3 weeks have been the worst of the winter, with a dozen other problems tossed in.  I could whine about it for hours...  :P

RedJoker

Yesterday at 12:05:32 PM
Hey Ag! I was just listening to your song "Incandescent." One of my favorites. Beautiful!
 

agradeleous

Yesterday at 11:06:04 AM
Morning hope all is well with everyone :) Joom you still shoveling?
 

whitestrat73

April 18, 2018, 06:33:03 PM
Yeah, musta been Neil....  ;D
 

papaG

April 18, 2018, 05:50:37 PM
Neil has been a little quiet. Lets blame him...
 

papaG

April 18, 2018, 05:49:44 PM
Wasn't me. We still have winter and snow neck deep. Too tired after shovelling....again....and again...but I did get invited to play a jamboree this summer ;D
 

whitestrat73

April 18, 2018, 02:06:10 PM
Wasn't me, Boss, honest. I wasn't anywhere near the drinks cabinet. I was miles away, musta been PG.....  ???
 

Joom

April 17, 2018, 09:41:35 PM
I've been so preoccupied with everything going wrong around here for the last week I hadn't even noticed, RJ.  I bet White caught it...

RedJoker

April 17, 2018, 06:31:11 PM
oops, I was just reading the text message that I copied into my previous 'shout' and realized my buddy used some colorful language.   :o  

I see someone already corrected it for me.  Sorry!!  :-[

RedJoker

April 16, 2018, 06:23:39 PM
I've been working on how to improvise and just found this playlist with a metric crap-ton of guitar backing tracks. Thought I'd share.

https://open.spotify.com/user/jafromonkey/playlist/5lthXOXhxhWEOFUJYaX9s5?si=jDPm9oByTgiy8ClIefhddw
 

Joom

April 16, 2018, 12:34:28 AM
Hey Hey, power back (for now).  But still snowing and blowing.

Wonder if Canada is getting any of this, or is it just our little treat?  :P
 

Joom

April 15, 2018, 09:16:53 PM
Well, heavy snow and 50mph winds with gusting.  Lost power about 6-7 hours ago.  Waited till it was 45 in the house to see if it would come back on before going out and starting the generator.  Hope it comes back on sometime tonight...

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Author Topic: Bassman to JCM Conversion Project  (Read 908 times)

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Offline gc

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Bassman to JCM Conversion Project
« on: October 09, 2017, 07:52:55 PM »
Just can't stop this guano.  Good for the soul.  Here are some pics on Imgur of the overall effort: 

https://imgur.com/a/u3a99

I had an old Fender Bassman 100 clone that was sitting around broken & waiting for attention.  Was going to 'restore' it but decided instead to rebuild it as a JCM 800.  I kept the 100w/4 EL34 tube configuration of the clone but have it running on 2 tubes for 50W. 

Using schematics & layouts from Marshall & Mark Huss, replaced the old eyelet board with a new Marshall 2203(100W)/2204(50W) layout, stuffed it full of components, rebuilt the capacitor 'doghouse' with values to match, fought power & ground issues & bad tubes & came away with a decent sounding amp.  Tranny's, choke & chassis about all that's left of the original.  Still cleaning up lead dress but it's pretty much all it's going to be.

Sweetwater had Celestion Seventy-80 refurb 12's for @ $30 USD ea, so I grabbed two & stuck them in an old cab.  Sound ok...see if I can break them in a bit. 

I never was much good at posting sound clips...but once again, I'll try to put something together & post it.

Regards,

Gordon

Online Joom

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Re: Bassman to JCM Conversion Project
« Reply #1 on: October 09, 2017, 09:03:21 PM »
Nice pics. GC.  And looking forward to the sound clips...  :)
A few quick and dirty cheaters from the old days, just for kicks...... www.twotrackmusic.com/joomcheats

Offline neilmac

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Re: Bassman to JCM Conversion Project
« Reply #2 on: October 10, 2017, 02:01:10 AM »
Looks the part....
Looking forward to the sound  ;D
"If it looks good, you'll see it.If it sounds good you'll hear it. If it's marketed right you'll buy it. But if it's real, you'll feel it"

Offline Jahva

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Re: Bassman to JCM Conversion Project
« Reply #3 on: October 10, 2017, 12:42:59 PM »
Oh that is an awesome idea and project...
Love the JCM 800 solid staple of Rock with Gibson humbuckers or the single coil Strats.
Good Luck with it GC.
Fight on brother!  ~:)
If.... it's a temporary lull... why am I bored right outta my skull?
Man, I'm dressin' sharp an' feelin' dull
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Offline frankenxtein

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Re: Bassman to JCM Conversion Project
« Reply #4 on: October 14, 2017, 03:27:52 AM »
Very nice  :) Do the Zeners get very hot?
Okay ... lets do this one more time ... take 43 http://www.soundclick.com/bands/default.cfm?bandID=1277143

Offline gc

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Re: Bassman to JCM Conversion Project
« Reply #5 on: October 14, 2017, 03:38:56 PM »
FX...yup, they get a bit hot.  Enough to give me pause & ask around a few places to hear others experiences with this method. 
Had a Bassman '100' clone from the 60'-70-2 sitting around, broken & decided to fix it.  Existing insides were a mess of broken/reuse parts & aged components.  Decided to reuse iron & grab what I had available for rework.  JCM 800 it is.  Had to put it together somewhat upside down & backwards & adapt the capacitor doghouse-can setup to fit.  Lead dress suffered accordingly but works ok.  Interesting 'make-do- project.

121VAC line voltage here.  PT tests out at 405-0-405.  That drops off 501+VAC at the rectifier bridge, 488VDC on the drop side (loaded with tubes).  W/O tubes I was reading over 500VDC at the B2+ cap (rated 500VDC).  Fixed bias w/o PT CT (pulls bias voltage off one PT HT secondary leg).  Zeners dragged it down to acceptable levels.  Price of power dissipation?    @116-120 deg F by my infrared rectal barometer, tubes in, sitting at idle.  Still in the shake down mode, so I'll see where this goes as far as longevity.  Works better than a dropping resistor.

Not used this method on this large an amp.  Not sure of how stable or trustworthy this will be.   Trying to get a handle on the amps 'tone'.  One really haws to lean on these to get 'that sound'.  And this amp doesn't even think about getting into it's groove until ear bleed levels..

Offline frankenxtein

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Re: Bassman to JCM Conversion Project
« Reply #6 on: October 16, 2017, 12:59:51 PM »
120.F doesn't seem that hot  8) Is this a old PT ?

Bucking a little of the primary goes a long way on the HT. From what I've read 6v is enough on the heaters so there's a juggling contest with newer transformers. Half winding on my 12vct bucking transformer gives me 115-116v. Take into account the bucking transformer has a 115v primary  :P 121-123v here on the outlet depending season and time of day. Really messes with my OCD when I check voltages in a amp  AM then do it in the PM.

 https://www.tubesandmore.com/products/transformer-hammond-filament-63-vct-4-open-style
Okay ... lets do this one more time ... take 43 http://www.soundclick.com/bands/default.cfm?bandID=1277143

Offline gc

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Re: Bassman to JCM Conversion Project
« Reply #7 on: October 16, 2017, 02:33:44 PM »
Yup...this is from circa 1960-70.  PT & OT are huge iron, built when men were men & sheep were scared.  And I'm really trying to get this to work & remain reliable using what's there.  Zener bridge is weak link & have yet to find a truly solid solution.  Zener works, but this is a rather large amp.  Still tinkering with the maths & Senior Ohms to see what science says.  But so far so good as far as holding up.  Bucking xformers, Variacs, dropping resistors, Mosfet ckts, even converting to a tube rect are considerations. 

Simple solution is get a new, correct voltage/rated PT.  Don't want to spend the $$$.  I played thru this for a bit yesterday at some volume & managed to see the temp get to 151 deg F.  Still not bad.  Still shaking down this sucker.  Never met a Zener that I trusted.

Tell you one thing though...even with the leads extended from the 'cap doghouse' and the overall compromise Marshall to Fender layout,this sucker is very quiet in the buzz & hiss dept.  Still trying to dial in the tone & gain.  Sensitive little thing, this.