What to build with this AO-29?

[Toxophilite]

So I'm going to use this nice long AO-29 chassis and it's accompanying cone boards to build something with a little more omph than the Ab763 deluxeI'm still going for clean headroom but maybe more around 30 -40 watts
Something I can use with my JBL D130
THey have pretty skookum PTs in these units and it's already set up for a octal rectifier and two octal tubes
I'll have to use an appropriately large OT as the one on there is a little tinyI want to include reverb and tremelo
Anyone have any excellent/ interesting recommendation??

[Toxophilite]

Just noticed it has a replacement PT9can see the different wires solder to stubs of the originals
With the 5U4˝b and NO other tubes in it's putting out 403 vdc...not a heck of a lot!
Maybe SS rectification would bring this up to 420-440

[sluckey]

With the 5U4˝b and NO other tubes in it's putting out 403 vdc

Don't measure the B+ with reference to the chassis. Instead, measure from pin 2 of the 5U4 to the CT of the PT HT winding. Even better, disconnect everything from the 5U4 socket except the 4 wires from the PT. Now connect a fresh 20µF cap between pin 8 of the socket and the PT HT CT. Measure the voltage directly across the cap. This will be your unloaded B+ value.

This circuit connects the CT to a resistor to develop a -22V to be used for fixed bias. This -22v will reduce the real available B+ by 22v.

[Ed_Chambley]

I built a 63 Vibroverb for a friend about 2 years ago.  I got a kit from Marsh as he wanted a stock reissue version.  Since them I have built 4 more in different configurations.  All were for guys who heard the first one live.  The original had 2 10's, but I did build one with a single 12 and used a Weber Cali speaker and sounded great.  I did build one for me finally and running through my 2, 12 Closed cab with JBL's it sounds wonderful.  The circuit has a nice breakup, but does clean up well.

Just a suggestion.  I like mine, but it is not my go to 6l6.  I have to admit with all the amps I have and play, my favorite is still the Blackface Super Reverb.  It does not have a cathode follower TS, but I have a Super Reverb that does.  I still prefer the plate driven tone stack even tho there is loads of insertion loss.  If I wan an amp to flat out jam, I use a decade switch and no Tone Stack.

Thought I would combine 2 topics.

[eleventeen]

I once owned a brown Vibroverb. It had JBL 10" speakers. It was pretty heavy. I was sure proud of it and it felt very cultish playing through it, but I never really enjoyed it as much I did ordinary blackface Twins and Pros. I can't say if it related to the 10" speakers, but I suspect this was the biggest element in my general apathy towards the sound of the amp----maybe they were too clean and brassy, being JBLs. I had lots of amps at the time and other than how it looked, this was among my least favorites. 

[TIMBO]

Hey mate, There was a guy in the UK, back MANY years ago that was running around at night and chopping up people and removing there ORGANS. I think his name was "JACK".

You seem to be harvesting quite a few ORGAN parts, SHOULD we be worried. 

Anyway, some pics would be great for layout ideas.

These amps are great and to transform them into a same old same old, but I would prefer to turn them into a ODDBALL, something you don't see everyday. 

[Toxophilite]

yeah
Look to your own organs!
I have only ever owned one fender amp in the last 25 years. My 1980 super reverb . A lovely loud amp for cleans
I can't afford to buy any of the ones that now have skyrocketed to ridiculous prices due to demand and nostalgia etc.
So I've been learning to build my own and I have no problem mixing and matching where it works!
Anything I build that's smaller than my super reverb is new and exciting for me!!

I don't think the PT on this amp has the poop for a vibroverb but with a better OT might make something along the lines of a vibrolux powers with either 1 x 15 (d130) a pair of 10s or a nice efficient 12
I haven't built an amp with reverb so that would be fun to try
I'm not worried about getting earlier breakup( nor hopefully is my girlfriend) I just want cleans in a smaller more lugaroundable package, reverb and tremelo too. I guess I could look into other designs(that use octal sockets(like ampeg maybe)
The brownface (A) harmonic vibrato sounds like a cool addition as well
I already have a pair of deluxes that work well for a quieter stereo rig
I loooove JBls!! Quality beeeaaauutiful sound!   but yes, heavy, and expensive unless you find them for a deal which is getting harder to do.

[Toxophilite]

Hey with the brownface amps that have the harmonic vibrato (like the 6G12A concert)
The vibrato circuit uses half a 12AX7, could one substitute a 6AV6 for the 1/2 a 12ax7??
Just curious

[TIMBO]

Sure can.

[Toxophilite]

Heck
I can't read that schematic
Does it require a specific schematic program?

[Willabe]

Here down load this, we all use it;

http://www.expresspcb.com/expresspcbhtm/Download.htm

[Toxophilite]

Heck again!
I'm on a Mac mini. The options seem to be for PC systems

[kagliostro]

Try with JSchem

http://dhost.info/jschem/

a Mac version is disposable

K

[Ed_Chambley]

Here is the schematic Timbo posted in a PDF for you.

[Toxophilite]

THanks very much everybody!


Is this a tremelo similiar to the one in the fender 6G12-A Concert ?
I was trying to see the similarities. It looks like it's own thing or a reworking of the circuit
Am I reading it wrong?

[sluckey]

Is this a tremelo similiar to the one in the fender 6G12-A Concert ?

Not even close, well, except they both use a phase shift oscillator to develop the tremolo signal.

BTW, if you are just looking at the pdf that Ed posted, you're missing most of Timbo's amp. Timbo's sch file has 5 pages of schematics plus one page for a voltage chart. Ed only converted the first page to pdf???   

[Toxophilite]

hmm
Though I have no personal experience with it..
The harmonic vibrato used in the brownface amps(that have an -A added to their name)
sounds interesting and might be a cool addition to my next build


The circuit uses 2 12AX7 and a half  12AX7 (quite large!)
I'd been understanding that the 6AV6 was half a 12AX7, and as my chassis has lot's of 7 pin sockets(most of which I'll be replacing)
I thought i could leave one and use a 6AV6 in lieu of the 1/2 12AX7


That was my question
also
Anyone have any up close and personal experience with this vibrato/tremelo circuit  ??
And is the sound worth the extra tubes, parts , work etc
Is it that much better than a standard bias vary like the 6G11?

[Willabe]

Or, you could just build Sluckey's revibe, which has the Fender brown face vibrato and spring reverb.

Then you can use it with any amp you have.

http://home.comcast.net/~seluckey/amps/revibe/revibe.htm


               Brad     

[Toxophilite]

That's a good idea
though I was hoping to reduce the number of components i lug around
So I was going to build an amp with reverb and tremelo


But maybe converting the standalone reverb I build in a Garnet chassis ,to a revibe would be a fun project as well


Though it's my understanding that the tremelo in the revibe is NOT the harmonic vibrato


Is that right?

[Willabe]

Sluckey's (and Doug's) are the brown face harmonic vibrato.


                  Brad   

[sluckey]

Though it's my understanding that the tremelo in the revibe is NOT the harmonic vibrato

It is a harmonic vibrator. It's an exact copy of the 6G12 circuit. And it sounds much better than the 6G11 bias vary tremolo. The 6G12 has a rich sound that's hard for me to describe but it definitely is more pleasing to my ears than the simple 6G11 sound.

The 6G12 only uses two tubes. The later 6G12A uses two and a half tubes. But the modulators (the important part of the sound) are identical. The 6G12 uses a paraphrase inverter but the 6G12A uses a cathode follower to drive a cathodyne phase inverter. They both do exactly the same, ie, produce two out of phase LFO signals for the modulator. The 6G12A  circuit maybe looks more better from an engineer's point of view, but they both function exactly the same.

You can certainly use two 6AV6s anywhere you would use a 12AX7. This circuit is no different.

[Toxophilite]

Cool!
Thanks
I'd somehow got it into my head that the harmonic vibrato was the 'A; circuit while the non 'A' ones were straight up bias vary
That sounds like a cool addition


Maybe a Ab763 or 6G-11 vibrolux power amp
a 6G-12 tremelo, Ab763 reverb
and a one channel AB763 preamp in front of it all
Maybe have a presence(NFB) control for fun too ala the 6G-12


All running into the JBL D130 for big clean sounds


Does that sound possible
Any conflicting elements there?

[sluckey]

Any conflicting elements there?

Probably. Look at the schematics of all those amps. I'm thinking you are pretty familiar with the AB763 by now. Look closely at how the vibrato is implemented in the 6G12. Then start thinking about how you will do the reverb.

[Toxophilite]

So the vibrato channel on a 6G12 goes straight through the vibrato circuit after the tone stack, in one end and out the other  mixing in with the other channel via a pair of 470k resistor then into the phase inverter


The Ab763 reverb takes a feed off the vibrato channel post tone stack goes through the reverb circuit and then mixes back in after a 10pf cap and a 3.3m resistor


hmmm


could you take a feed off the tremelo into the reverb or would the gain be wrong?


or visa versa?


Would the two effects do funny things to each other??


i guess the design advantage of the bias vary 6G11 is that it's really not in the audio circuit at all

[Toxophilite]

Could one take the signal from the tone stack and split it into the two effects and then mix it back together, somewhat similar to the revibe?

[Toxophilite]

So is it an impossibility to use the Ab763 or in the case of the vibrolux AA964 reverb with the 6G12 concert's vibrato?
My instinct would be to try and use a layout similar to a revibe but after the tonestack
crazy? impossible? fraught with disaster?
Has anyone tried this?


Interestingly(referring to a previous posting by S Luckey)
With an SS rectfier
when I measure the B+ from pin 8 of the rectifier to the green heater centertap(which is hooked to the chassis )
with pin 8 still attached to the resistor prior to the first filter cap
I get 417 vdc.
If I disconnect pin 8 of the recitifier from the resistor..it drops to about 365vdc
If I measure across a 20 us cap going from pin 8 to the HT CT with pin 8 disconnect from the resistor..I still get 365vdc
Maybe this PT doesn't have the poop ??
Checking the AO-29 schematic seems to confirm this.

[sluckey]

Interestingly(referring to a previous posting by S Luckey)
With an SS rectfier
when I measure the B+ from pin 8 of the rectifier to the green heater centertap(which is hooked to the chassis )
with pin 8 still attached to the resistor prior to the first filter cap
I get 417 vdc.

That's the wrong center tap! I said...

"Don't measure the B+ with reference to the chassis. Instead, measure from pin 2 of the 5U4 to the CT of the PT HT winding. Even better, disconnect everything from the 5U4 socket except the 4 wires from the PT. Now connect a fresh 20µF cap between pin 8 of the socket and the PT HT CT. Measure the voltage directly across the cap. This will be your unloaded B+ value."

[Toxophilite]

ooops
Well there was no smoke
It was all the abbreviations that got me confused HT CT PT TNT LSD CCCP

Thanks


i just tried it using the points you illustrated with a 22 uf cap across them and got 363 vdc


Interestingly enough on the schematic it has the B+ being taken off of pin 2,  on the amp itself they're using pin 8


Here you can see the obviously replaced PT. It is a Hammond Organ PT.  AO- 24157-2..which from checking is almost the same part number as my AO-43 chassis  AO-24157-1

[sluckey]

i just tried it using the points you illustrated with a 22 uf cap across them and got 363 vdc

That's odd.

Try this with everything connected normally. Measure voltage between chassis and pin 8 of the rectifier. Should be some positive voltage. Then measure voltage from the HT CT to chassis. Should be about -22vdc.

[Toxophilite]

SS rectifier plugged into 5U4gb socket(NO other tubes in) pin 8 of rectifier hooked up to red wire leading to reesistor and then to the isolated can cap that has the HT CT




"Measure voltage between chassis and pin 8 of the rectifier. Should be some positive voltage."    420vdc


"Then measure voltage from the HT CT to chassis. Should be about -22vdc."      - 7.8


If I disconnect the wire to pin 8 of the rectifier voltage at pin 8 drops to 347vdc

[Toxophilite]

I don't know if it helps, but with no rectifier in I get 320 AC on the secondaries

[sluckey]

All those voltages are believable. The -22v is low because it depends on the current draw of the amp. With no tubes in, the current draw will be very small, and the -22v will be small also.

The voltage on the rectifier drops when you disconnect the wire to pin 8 because you no longer have a cap to charge to the peaks of the rectified AC pulses. So, instead of a nice smooth dc voltage, your meter is now trying to measure the average of the rectified AC pulses and that will always be less than the peak.

I kinda struck out on a tangent with this project. I think the PT is probably fine for what you are thinking about. Sorry for the side track.

[Toxophilite]

No problem I was just getting back to a previous posting and following up on it
Thanks


What do you think about the possibility of an unholy coupling of the AB9964 with a 6G12 vibrato??

[sluckey]

What do you think about the possibility of an unholy coupling of the AB9964 with a 6G12 vibrato??

I don't know what an AB9964 is, but I thought your other ideas about AB763 with reverb and 6G12 vibrato is very doable. I also think it's a very ambitious idea that will require a LOT of planning, then a LOT of building. And you have to plan on having to fine tune everything once it's built just to get the two circuits intergrated properly. The results could very well be your holy grail!

I would start by blending the two schematics together. Plan to spend a lot of time at this phase.

Once I had a schematic that seems to work on paper, I'd begin work on the layout. Plan to spend a lot more time at this phase.

After investing so much time in these first two stages, I'd probably rip the iron off the AO-29 chassis and start with a virgin chassis (maybe 22 x 6.5 x 2.5)  that is a good size to work with my layout.

Or I might just build a revibe!   

[Toxophilite]

ooops
I meant a AA964 like the vibrolux reverb
My apologies for the typo


I'l get planning I guess and put forth some ideas


The revibe is very temping but I was hoping to reduce the amount of gear I carry
Also I'm not keen on the way the 6G15 rolls off the top end of the dry sound

[Toxophilite]

Could this work??