Blackfacing a 69' Twin

yups.. he's actually fixed a couple of guys amps.. eg. kennethc's hotrod deville. But my dad is old and get's tired abit easily so we have to take it one amp at a time.. lol.. he was one of the best tube/electrical engineers in his time in Singapore(personally i believe he was THE BEST) and now that he's retired this is just something i try to keep him occupied with so he doesn't get too bored at home.. I guess if you guys need any help with your tubes you can always pm me.. he's always willing to help.. just that can't take too many jobs on at one go.. :)
 
personally i believe he was THE BEST
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Awwww i am all fuzzy now .... :D

I believe your dad will have more patients dealing with those ol' amps. Restoration is a painful and expensive task but weilds sweet satisfaction ....

I just got my MusicMan mod and semi restored ...i am a happy man !!
 
Nice nice! The more of us the better! :)

Guitar Tubeamps especially the original 1st generation types like the classic Twins and Plexis went through many revisions along theway to keep up with the changing demands and trends. Schematics available to the public serve mostly as a guide to the original design but unless one can get hold of the official manufacturers rework and update sheets. Servicemen and modders have to rely on know how together with either word of mouth, the internet or summon the mojo spirits for help.... Hehe :)

Personally, most of the original tube amp designs by Fender, Marshall and Vox were already pretty spot on and will remain that way for a long time... I feel. The materials used and low tolence ratings of certain critical electronic components from yonks ago were part of that Mojo in these amps. Also sad but true that some are now extinct like the Sylvania tubes. Last heard Peavey bought off all remaining stock of the Sylvanias for the 5150.

The revisions that came along the way are usually motivated by a fair mix of well intended sonic tweaks and the original maker's right to incorporate changes to parts or redesign to create more cost effective manufacturing.

If must try at first to restore the amp to it's original specs to appreciate and experience the original intended design before implementing mods. You may just surprise yourself.

:)
 
hey thanks for dropping by Randolf! Nice to hear your comments! :)

Think I need the mojo God's help if I want to take it further.. :)
 
Hey Indigo! :)
Blackfacing would be fun but hey the Silverface is also a classic sound in it's own right ya. Stay safe and enjoy the project and the sounds mate! :)
 
yeah thanks Randolf! Silverface has got its own mojo alright!

Some more comments on the blackface sound.. on my bridge humbucker, there are way more harmonics than pre-mod.. the harmonics are really fierce man.. but on single coils the sound is tamed..

the amp seems to be a bit gainier now as well.. with my trusty OD-3, I can get a nice verge of break-up even with drive set to minimum on single coils when i play hard rhythm.. i don't remember it being so previously.. its nice though.

the amp definitely feels 'livelier' and 'lighter' now. Pre-mod it felt slightly 'heavier' with more thump and bass. Now it feels more organic. The slightly lower bass response may not be a bad thing..

I still think changing out those old oxford speakers will really bring out the full character of the amp.. again maybe later.. :)
 
Nice!
Now that the amp is running along sweet experiment with speaker types and wattage ratings to experience whole wide world of different tones from the amp and the cab design. Tube amps are simply wonderful. :)
 
Just a quick update.. the tremolo circuit in my twin has been fixed :) Thanks to goose' recommendation on a website which sells opto-couplers I ordered a new one in for about $35.. my dad replaced the old one with it and voila the tremolo is working!

We also looked through the caps again and realised that we had wrongly replaced a 0.1f cap with a 0.047f cap in the pre-amp circuit.. this had resulted in the loss of bass response i reported previously.. well we got it right this time and all the bass is back in all its glory.:)

We had also missed out the cathode bias cap and resistors that had been attached to the power tubes in the AB568 circuit..(these are not found in the 'usual' AB769 circuit). Well, we promptly snipped these off resulting in a fully fixed bias amp true to blackface spec.

Verdict on the blackface sound?: Two Thumbs up. :)
 
Awesome...pics pics :D

Btw... please keep the preamp gain *just nice* if you are wanting to up the gain ! ....we don't want a squealer :lol:

Check what i got from another forum....
the Fender blackface/Silverface and the Fender Tweeds are two different animals, and within each family, there are quite a lot of different sounds too. The main differences are in the arrangement of the stages, and in the votlages used.

If you run a preamp stage at a higher voltage like a Blackface amp does (Silverface is even higher), you get more gain, and more headroom in that stage. Keep in mind that gain and distortion/overdrive are not the same thing. The larger blackface amps like the twin reverb are running around 220v on the preamp tubes, which gives them more headroom, allows them to accept a larger input signal without distorting, and gives them more gain so they amplify the signal more. The tweeds are more like 150-170v, which takes the gain down a bit from each stage, causes them to overdrive sooner, and the can't take as large of an input signal, so they will distort easier if one stage is overloading the next.

The other important thing is the arrangement of the stages. Most of the tweeds are what is considered a 2 + 0 setup, and most of the blackface amps are a 1 + 1 or a 1 + 2(bassman heads) This refers to the arrangement of the gain stages in relation to the tone stack. The tweeds have two gain stages before the tone stack, and the blackface silverface stuff has 1 before the stone stack, and either 1 or two after it. The tone stack sucks a lot of gain away and in the tweeds a cathode follower circuit is used just before the tone stack to keep as much gain from getting lost as possible. The output of a cathode follower is low impedance, which allows the tone stack to work better, and allows more gain out of it. In the blackface amps, they take the signal off the plate of the tube, so it is high impedance and the tone stack sucks a lot of the gain away and doesn't work as well either. BUT, since the tone stack in the blackface comes after only one stage, it works better than the tweed setup because there is less overdrive at that point in the circuit arrangement. Also, the settings of the controls on the blackface determines how much signal gets to the following stages and gets amplified a lot more than is the case on the tweed stuff.

You could change the tone stacks around, but you wouldn't get the full effect unless you changed the arrangment of the stages, and reduced voltages to a given channel's preamp tubes. This is a lot of work as currently the preamp channels share power supply nodes, so you would have to seperate them by adding several caps and resistors with their values chosen so they get you the correct tweed voltages. You would also have to change the existing ones on your blackface/silverface channel because now that the load is different on these since you've removed some tube stages from them, the voltages will rise and get them even more clean than they are now. You can leave all that as it is now and just change the values in the tone stack and it will just change the frequency response of the tone stack and shift it one way or the other. Check out the tone stack simulator on this site...its pretty useful for amp work and you can see how the tone stack works. Its a free download.

http://www.duncanamps.com/tsc/index.html

While you can mess with the amp and channels to get the character different, if your main goal is to get it to break up sooner, I would do two things.

1) disconnect the negative feedback loop

2) change the dropping resistor values for the preamps to a higher value so that the preamp voltages will be lower. This change more than anything will brown the amp up and get it to overdrive sooner. Greg Simon
Click to expand...
 
Useful info :)

I bought a book recently which details how to convert a channel on any silverface/blackface amp to tweed specs or even marshally spec using the vibrato tube... :)
 
wow Indigo, your dad rocks!! :supz:

nice twin you got there.. since we're on the topic of old fender amps, let me share some photos of your amp's long lost older cousin.. also recently restored..

P1060324_edited.jpg


P1060322_edited.jpg


its an early '67.. still has its 4 original alnico speakers.. :D
 
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