6G6B build done

ToneMerc · Post by **ToneMerc** » Wed Sep 19, 2012 11:27 pm

Started on this build for a friend. It a basically a 6G6B with a tube rectifer and a revoiced bass channel.

Chassis & faceplates: Marsh

Iron: custom Heyboer PT setup for modern voltages with an extra 6.3V tap, the OT is a MCI M6 Bassman. Down the road if he chooses, I can upgrade it the MM blone iron.

Modern upgrades: modern bias supply with bias pot relocated to the rear of the chassis and shielded coax on the inputs. The cap bank had balancing resistors and is 40-20-20-20-20

Glass: he had to have tube rectifier(GZ34), but I will also include a s/s plug in.
TS RI 5881
balanced LPS and JJ883's in the front

Signal caps & resistors: yellow Sozo's, Speer KOA CF and CCF60 metal film.

TM

alvarezh · Post by **alvarezh** » Thu Sep 20, 2012 6:37 am

HI TM, you have stated that you have built a few of those, here is one I did last month for a friend.

No need to tell you about the parts used, I have noticed from your posts that you are way much more knowledgable on figuring them than me. The filters and the little bulbs(which are covered) are Spragues and JJs.

One thing, as you have probably noticed, is the use of the Koas all around, was afraid of getting too hissy with MFs. I refurbished a Twin for another friend before my build and I installed Dales a la Dumble but you could hear the fingers moving on the strings too strongly. I installed the Koas and it was less notable, so I didn't want the same thing to repeat on the Bassman.

You do great work!

All the best.

dcribbs1412 · Post by **dcribbs1412** » Thu Sep 20, 2012 5:03 pm

Looks great guys...
I have some Bassman iron sitting here.
Might be time to try one.
TM, are you putting a switch for SS/ Tube rectifier?

Wondering what KOA's you are using alvarezh
I have used the green CF ones but not sure which ones yours are.
Do you have a part #?. Build looks really nice BTW.

Darin

alvarezh · Post by **alvarezh** » Thu Sep 20, 2012 5:14 pm

Thank you Darin, here are the Koas:

http://www.mouser.com/ProductDetail/KOA ... 2bFWOGxedB

The 682 represents the value 6.8K for this specimen.

Also, I used FREDs, here:

http://www.mouser.com/ProductDetail/Vis ... lOJMUjHBOe

All the best!

Phil_S · Post by **Phil_S** » Thu Sep 20, 2012 5:35 pm

I am a big fan of putting the filament harness in the air. I like your execution of that style of lead dress. It looks great. I can't see; how far up above the tube sockets does it rise?

My skills are not at your level (yet), but I also wire the filament harness first. I'm glad to see an experienced builder like you does that.

Thanks for showing us!

ToneMerc · Post by **ToneMerc** » Thu Sep 20, 2012 7:25 pm

dcribbs1412 wrote:Looks great guys...
I have some Bassman iron sitting here.
Might be time to try one.
TM, are you putting a switch for SS/ Tube rectifier?

Wondering what KOA's you are using alvarezh
I have used the green CF ones but not sure which ones yours are using.

Darin

Thank Darin, not on this one. For my personal build, I was going to mount the tube/s/s rect at the "ground" switch location but I scratched that idea and went solely with s/s. This build, he was stuck on the tube rectifier and adament about not wanting to have remove the chassis from the box to check bias. Thus, to make it easy for him I mounted the bias pot at that location.

I'm using the Speer/KOA SPR2CT.

TM

ToneMerc · Post by **ToneMerc** » Thu Sep 20, 2012 7:27 pm

Phil_S wrote:I am a big fan of putting the filament harness in the air. I like your execution of that style of lead dress. It looks great. I can't see; how far up above the tube sockets does it rise?

My skills are not at your level (yet), but I also wire the filament harness first. I'm glad to see an experienced builder like you does that.

Thanks for showing us!

Thanks Phil, I'll see if I can get you a side profile of the heater string.

TM

ToneMerc · Post by **ToneMerc** » Fri Sep 21, 2012 12:50 am

Phil_S wrote: I can't see; how far up above the tube sockets does it rise?

Phil, the string is around .600 above the socket solder lugs. For me, I always find heater strings as my weakness, but I think I'm getting better over time . Generally with Marshall and Fender types I install the heater string very early on. However, with Dumble style builds, I work the chassis perimeter CCW, CW, CCW and then CW taking care of all the perimeter parts and then overlay the heater string maybe 40-60% into the process.

Mike

ToneMerc · Post by **ToneMerc** » Fri Sep 21, 2012 1:21 am

alvarezh wrote:HI TM, you have stated that you have built a few of those...................

You do great work!

The first one was personal build, but I broke one my #1 rules on project management .......have parts in hand, mock up and verify fitment beforehand

Semi long story; I used a chassis that wasn't exactly a blonde clone chassis to layout boards and build my boards up. Well when the face and backplates came in they didn't line up. No worries, I'll just get the clone chassis and drop in my boards. Dang, my cap and preamp boards have different mounting and pass through holes from the correct chassis. Thus, I dropped that project and will revisit it sometime.

Hey, thanks for sharing your build. I learned something from you too. I relocated my choke pass through to the same location as yours. As soon as I saw your picture, I went now that's a better location.

Mike

Phil_S · Post by **Phil_S** » Fri Sep 21, 2012 2:14 am

Thanks for the heater close up. Very nice work. I think maybe I need some new and different shaped pliers to knit the wires so nicely at the sockets. I think maybe I allow mine to rise higher than necessary. This was really good to see.

alvarezh · Post by **alvarezh** » Fri Sep 21, 2012 3:00 am

Thanks Mike for the explanation on the previous built. A few extra holes is no big issue, it's not a boat or a pressurized airplane!

BTW, I just noticed that the image shown is not of the final amp, let me explain.

1) the resistor paralleled with the bias cap is an error, I don't know what I was thinking when I did that.

2) the heater voltage was very unbalanced, so I eliminated the center tap and installed a pair of 100r resistors by the pilot light. Fender installs the pilot light base to the left sidewall of the chassis mine is installed against the top, you have to do some bending but this way you can place the contacts 180 degrees apart, IMV just safer.

3)I installed the treble bleed resistor across the V2b plate resistor as per the original schematic.

Notice I ran the B+ to V1b from the outside of the chassis (very short yellow wire). I believe Fender ran it inside underneath the main board, guess that's a safe thing to do in a country where any excuse is a good excuse to meet you in court.

Glad to have been of help on the choke issue….. to an experienced pro!

All the best!

@ Phil, I use a Mini vise, Clamp the two wires to it, now you have both hands free to turn the wires without tools. I make few turns and pull the wires out to tighten the twist.

It's not the one I use but here is one for a nice price:

http://www.amazon.com/Mini-Table-Vise-E ... bench+vise

Cheers!

Roe · Post by **Roe** » Fri Sep 21, 2012 6:18 pm

alvarezh wrote:T...

3)I installed the treble bleed resistor across the V2b plate resistor as per the original schematic.
...

Cheers!

do you prefer the 2nf cap? have you tried 1nf or 500pf?

alvarezh · Post by **alvarezh** » Fri Sep 21, 2012 9:25 pm

Roe, I didn't experiment much, but I noticed it had too much treble when I tested it so I installed the cap. Much better after that, but the amp is not mine and I don't want to accustom my friends to custom voicings because they hardly ever stop or get satisfied, at the end of the day they want a Blonde Bassman to sound like a BF Twin with a Strat and like a Plexi with a L.P.

I can tell you this: for my taste, it's still too trebly even after I installed the cap. I would experiment with the lower value (just as you suggest), maybe will dump less mids and lows to ground. Also the speakers may have their take on this too, it's got Jensen C12Ns.

Sorry I could not be of much help on this, maybe Mike can chip in since he's got more experience.

All the best.

Phil_S · Post by **Phil_S** » Fri Sep 21, 2012 9:54 pm

alvarezh wrote:Phil, I use a Mini vise, Clamp the two wires to it, now you have both hands free to turn the wires without tools. I make few turns and pull the wires out to tighten the twist.

Horatio:
Not sure I understand. Do you measure and cut the twisted pair first? Then you build the assembly outside the chassis? Then you install it?

I've always just done it on the fly inside the chassis. Should I be thinking about a change in method?
Phil

alvarezh · Post by **alvarezh** » Fri Sep 21, 2012 10:31 pm

Correct Phil, I do section by section.

First of all you have to take into account that as you twist the wires they shorten so you need to cut the wires twice the needed (twisted) length, that should also give you enough free wires for both down legs into the tube bases. Once you get good at it you could probably use shorter wires as you would know how much the total length shrinks after twisting.

Leave about an 1-1/2 to 2" of free paralleled wires in the clamp, then start turning until you get the desired distance of twisted pairs (this would be the center distance between two tube bases) and cut off the other ends about 2" of straight pairs. Bend both ends 90 degrees down into the tube, adjust length of free ends of straight pairs of wires as desired. Mine stand about 1/2 to 3/4" above the top of the tube base pins when finished.

It takes a little practice, you could probably make a few ones too short at first, then you will get good at it.

Hope I am clear enough, if not, ask again for any clarification.

All the best.

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