Conn organ just landed in my driveway.... Beginning the Saturn V build.

[1blueheron]

So a guy gave me a Conn organ last week just for hauling it away.  He probably would have paid me if I had asked.    I got it home and broke it down over the weekend.  Appears to be full of goodies.

I would like some ideas on re-purposing this as it is not your everyday amp.  I did a search and found a discussion thread on it that I can't seem to find again but it indicated it was actually 2 or three amps all based on a single chassis.  One small amp section using 12V6 to drive the High freq. section and a slightly larger amp for the low freq. section using 6L6.  Also supposed to be a trem driver loop using the other 2 -12V6's?

Is anyone familiar with this?

Everything appears to be in pretty good condition and all the tubes lit when plugged in although it didn't have much volume.

Only visible issues are the power cord which is dry rotted and the two wires in the picture which appeared to be scorched and a couple small rust blisters on the chassis.

I assume there is a reason that the resistor is getting hot enough to char these wires and something needs replaced besides the wires? 

Don't want to plug it back up and check voltages etc. if there is something that needs to be attended to.

[1blueheron]

Here is a schematic that appears nearly identical,mine uses a single 15" instead of the 2 -12" speakers

[1blueheron]

location of the toasted wires

[terminalgs]

I would like some ideas on re-purposing this as it is not your everyday amp

before modifying, I'd fix the wiring issues and see how it works 'as-is'.  plumb an guitar input to those 'S' and 'T' inputs and figure out the trimmers and pots.  see if you can make either or both of the power amps sound good as-is.


don't worry about the pair of 12V6GT's V12 and V13, their load is connected via connectors 25,26,27 in that dotted line box., so if that connector isn't connected there will be no VDC on the plates of the 12V6's.


if you can't get a speaker load on both power sections, remove the power tubes from the one you aren't using.  since you got the entire organ, hopefully you still have the speakers and figure out the load impedance the OTs want to see.

[1blueheron]

Yes, saved all the speakers but the 5-1/4" speakers on the "t" section are field coils. and had a strange rats nest of wire taped on two large caps.    The 15" reads 7.8 ohms across the bare terminals.  Might replace those wires and put a new 3 prong power cord on it tonight if time allows.

[DummyLoad]

I would like some ideas on re-purposing this as it is not your everyday amp

before modifying, I'd fix the wiring issues and see how it works 'as-is'.  plumb an guitar input to those 'S' and 'T' inputs and figure out the trimmers and pots.  see if you can make either or both of the power amps sound good as-is.

TGS, i don' think that will work work out too well, unless, he has the expression controls plugged in. U1-U5 are the volume pedals (expression controls). so, unless you have the whole organ and the pedals wired to the chassis plugging into "S" and "T" will not amplify anything.

--pete


EDIT: just junper U1 to U2 and U3 to U4 - use the guitar volume control.

[1blueheron]

I have not thrown anything out or fully butchered anything up yet, just removed it from the case.  I still have the intact expression pedal which is pretty cool in its own right.  I can just plug that back in.  Didn't get around to replacing the wires and cord last night.  Maybe tonight.  Anyone understand exactly how the tremolo circuit worked on these things?  I assume that is the "T" side and also handled the mid/high frequencies. 

[terminalgs]

those two amps in the schematic are nearly identical except for the NFB networks R16/R20 and R30/R34 (and based on the pictures, the OTs are different (at least in size). so if the tremolo signal comes in on 'jack t' it is coming in already "tremolo-ed" (so the trem is handled @ in some other chassis).


Also of note: besides the OT, and NFB, the B+ supply to the power tubes is different.  It might be fun to make it into a stereo amp, but you'd have to sort those details out to make them match...

[PRR]

I'd want more detail to even guess how the trem works.

When you said "field coil" I said "yeah, not!" but indeed: the "output transformer" for one channel does appear to be field windings on the small speaker. Which is in a box. Modulating field current would modulate speaker sound output. But what is the "T" input? Organ, or a slow-rate oscillator?

There were MANY "Conn organs" so I'm not even going to search without a model name/number.

[SoundmasterG]

Conn made good quality stuff. Many of their amps used Foster transformers (great quality according to Andy Marshall from THD) out of Cincinnati, (company still around though no idea if they still do tube amp related stuff, EIA code 394) and some others used Schumacher, or combinations of both. The 3 power amps in one chassis thread that I posted about that you mentioned had one power transformer and three output sections with their own transformers and all were Foster except the smallest output transformer. Yours is obviously different than that, but if those are Foster transformers you might be able to contact them and get some of the original specs of the transformer. That was what I did with my amp and they were VERY helpful, though that was the late 1990's when I asked them about that.


I agree with the others that you should get it working first and then decide on a plan to mod. It looks like you have a lot of room on that chassis to add in a nice guitar amp though I think maybe you might want to reorganize the layout a bit if that is what you decide to do. A stereo amp is a good possibility too. Nice score!

Greg

[1blueheron]

I'd want more detail to even guess how the trem works.

When you said "field coil" I said "yeah, not!" but indeed: the "output transformer" for one channel does appear to be field windings on the small speaker. Which is in a box. Modulating field current would modulate speaker sound output. But what is the "T" input? Organ, or a slow-rate oscillator?

There were MANY "Conn organs" so I'm not even going to search without a model name/number.

Sorry, I guess I did leave out that key peice of information...   
It is a Conn "Serenade".  Model #621-F.  From what I gather it was built somewhere between 1958 and 1961.

There are 3 small speakers.  Two 5.25" and what appears to be a 6X9.  Both of the 5.25" speakers were mounted on the expression pedal box and both of them utilize field coils. The 6X9 is upward firing through the top of the organ.   

The phono plugs at the "T" and "S" inputs run up to a connection strip that the all of the stop selectors are wired to using shielded wire.  One connects near the tremolo selector and the other near Tibia.   From there I have difficulty following it.  They appear to have used tuneable coils in the oscillator circuits each one has and adjustment screw.  There are several rather large ones mounted on either side of the 6X9 speaker.

This thing is jam packed with BlueMolded caps.   A dozen or more in each of the ocillator modules along with six 12AU7 per module.

Will post more info and pics as I test and dissect.

[1blueheron]

Just finished replacing the two toasted wires.  The red one actually fell apart in the process of removing it.  Not sure how it was still working.  The violet wire was still intact but barely.  Also got a new 3 prong power cord installed.

I have all of the old cables and connectors re-installed and am in the process of tracing where they went.

The 6X9 speaker is not on the schematic and as I mentioned, I have a single 15" rather than 2-12"

I appreciate the feedback so far.

Oh yeah, the PT has K59094 2  stamped on it. Under those numbers are A   9   13

The OT with the doghouse on it is stamped K58054-2

The transformer without the doghouse is stamped K58459 and under that number is 606938

[1blueheron]

Connected the expression pedal, hooked up speakers to both channels, connected the remote power switch and plugged a tape and deck into the RCA inputs at T and S.  Powered it up and I have no output to the speakers.  I think I am missing something.  Some kind of remote switch, loop, or something that isn't on the chassis and needs to be connected.

I could here sound emanating from the tubes but nothing from the speakers.  Speakers completely silent, not even hissing.

[SoundmasterG]

Are there any other numbers stamped into the transformers? Those numbers with the K are likely just a product code from Conn. The one with the 606 on it is a Schumacher as 606 is their EIA code.


Sometimes they would have a connector that went out of the chassis through some connection that gets completed back to the chassis when something else is connected. Kind of like Ampeg did with the Portaflex.


Are there any molex plugs or 8 or 11 pin connectors that have wires going to them inside the chassis and then have a plug that would connect on the top of the chassis that would go somewhere else?

Greg

[DummyLoad]

PT getting power? filaments lit? voltage readings?


--pete

[1blueheron]

Are there any other numbers stamped into the transformers? Those numbers with the K are likely just a product code from Conn. The one with the 606 on it is a Schumacher as 606 is their EIA code.  Will check again. Those numbers were on top.


Sometimes they would have a connector that went out of the chassis through some connection that gets completed back to the chassis when something else is connected. Kind of like Ampeg did with the Portaflex.  I think this is the case.


Are there any molex plugs or 8 or 11 pin connectors that have wires going to them inside the chassis and then have a plug that would connect on the top of the chassis that would go somewhere else?Yes. Several octal base plugs that do this.  One is listed as internal SPKRS and has 3 connectors stacked. This is the one both speakers were originally connected to on the top connector.  One is listed as external spkrs and then there is the expression pedal.  I know the expression pedal is connected correctly as there is only one way to connect it.  The top of chassis connectors also have orange, black and red wires that were connected to other parts of the organ.

Greg

Thanks for reply Greg,  answers in red.

Dummy Load, Yes, there is power to the PT.  OA3 is glowing brightly, filaments are lit on all the tubes.  I need to look closer at the 5Y3. didn't seem to be lit as obviously as others.  Planning to take voltage readings next.  My concern is if for some reason the speakers are not connected due to an open loop off chassis, I don't want to burn up the OT's.  Should I worry about this?  Just pull the tubes and do voltage check without them?

[DummyLoad]

pull the output tubes if you are unsure of the load.

if you are unsure of the speaker connectors, and want to check with a load: clip in a speaker on the main amp with some test leads, with just those two power tubes installed.


--pete

[SoundmasterG]

Thanks for reply Greg,  answers in red.

Dummy Load, Yes, there is power to the PT.  OA3 is glowing brightly, filaments are lit on all the tubes.  I need to look closer at the 5Y3. didn't seem to be lit as obviously as others.  Planning to take voltage readings next.  My concern is if for some reason the speakers are not connected due to an open loop off chassis, I don't want to burn up the OT's.  Should I worry about this?  Just pull the tubes and do voltage check without them?

With no signal you can run the amp without a load without issue. Obviously though if you are trying to get sound out of it, then you are running a signal through it, and then you will need a load. Pulling the tubes is a good place to start to get some voltages, and then you can check again with tubes in and no signal.


It should be possible to trace where the wires and connections are going to see where the load is supposed to be.


Greg

[1blueheron]

Had a chance to do some more testing on the Conn.

I am 99% sure all the tubes were lit when I powered it up to take readings.  After I was done, I shut it off then powered back on again, at which time I noticed that the 5Y3 and one of the 12V6 tubes were not lit.

Swapping sockets on the 12V6 the problem moves with the tube so I will need another 12V6.  A 5U4 will light in the 5Y3 position so it looks like a bad 5Y3 as well.

Readings were as follows:

[sluckey]

You have 433VDC on V2 pin 8. This means your 5Y3 filament is lit and properly heating the tube. It's not always easy to see filaments inside a tube. I bet it's warm to the touch. I bet if you turn off all the room lights you will be able to see the 5Y3 filament. Anyhow, that tube is fine. Let it be.

[1blueheron]

You have 433VDC on V2 pin 8. This means your 5Y3 filament is lit and properly heating the tube. It's not always easy to see filaments inside a tube. I bet it's warm to the touch. I bet if you turn off all the room lights you will be able to see the 5Y3 filament. Anyhow, that tube is fine. Let it be.

It must have stayed up long enough for me to do my voltage check and then died or have some kind of weird intermittant issue because the 5Y3 it is stone cold dead now.  No voltage on Pin 8, cold to touch,, no visible filament glow even with lights off.  Anything I should try or test or call it a bad tube and move on?

I am thinking this chassis might be an ideal candidate to build the Reverberocket on that I previously wanted to build.  It has enough sockets, Enough power and tubes aren't far off from what I would need if I am thinking right.  If I go in this direction, do I really need tw rectifiers?  Can I get by with just the 5U4 and forget the 5Y3?

[shooter]

Can I get by

This is where math comes in 
what is the system load?, is the XXX tube up to it?, can you find other amp builds of similar ilk that do it?

(re)-design, take more effort than, Step 1 solder...., but that where the fun is 

[1blueheron]

Yeah, I was never a star student in math

Right now I have two differrent thoughts in mind for this amp.

Plan 1:

Reverberocket R12R.   Specifically the below version.

https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_r12r_reverb_rocket.pdf

Remove all of the 12V6 tubes and use those octal sockets for 6SL7, 6SN7, 6SN7,  6SL7 re-wiring them for 6.3 v heaters.  The 6L6 sockets would then be re-wired for 12V heaters and two of the removed 12V6's would become the power output tubes.  The small noval tubes would no longer be needed or they could be used as an optional high gain pre-amp section or for FX loop. I know this would pretty much be a gut and build operation.  I am pretty certain that just the 5U4 would be able to support this as it is beefier than the 5Y3 which ran all the 6v6 Reverberockets correct?  Or I guess I could get a new 5Y3 and run it like the true Reverberocket was set up.  I think the only parts needed here would be some Pots and the 6SL7 tubes.

Plan 2:

A combination of the  Egnater Rebel 30 and the Ampeg Super Echotwin.  This concept would leave everything pretty much as is.  A 2 channel amp with the 12V6 channel for a "dirty" side and the 6L6 side as the "clean" side and coming up with a way to blend the two for a combination of sounds.   The modifications needed here would be creating the ability to send a single input signal to both channels at once.  Rather than use a "Mix" knob like the Egnator, I would just use 2 separate speakers and use the "balance" volume controls already on the amp to determine the level of dirty and clean mix unless someone is aware of an easy way to mix the two output signals similar to the Ampeg Super Echotwin.  I could probably even use the existing tremolo circuit to do something similar to what the EchoTwin did.

Thoughts?

[sluckey]

Plan 1, the Ampeg R12R, would be easy to build in this chassis. Your plan 2 would be a bit more of a challenge but should be doable also. But, before breaking out the soldering iron, you need to spend a ***LOT*** of time on the drawing board.

First, put together a good working schematic. This is already done with the R12R.

Second, develop a good layout from your schematic. I suggest a board type layout. The board layout has to work with the tube lineup as well as the front panel controls. I don't recommend trying to do a PTP build (like your last project). Board layout is much easier and neater, especially since the tube sockets are lined up along the back side of the chassis. It would be helpful to study some of Hoffman's layouts, particularly the single channel AB763 because it has a reverb and a tremolo circuit. Your layout would need to be a bit different, but the general layout could be very similar. Being able to relate your layout to the schematic is very important, almost as important as reading/understanding the schematic.

You will spend much more time on the drawing board than you will on the workbench. Once the first and second steps are satisfactorily done, you can proceed to strip the chassis of everything except the transformers and tube sockets. ***NOTE*** The OT needs to be relocated toward the PT and near the output tubes. It's currently sitting where your inputs and preamp circuit should be.

Finally, begin assembling the R12R.

………………………………………

A little info about your rectifier and filaments... First, the 5Y3 only supplies power to the 6L6 plates. Nothing else. The 5U4 supplies all the remaining circuits, including any off chassis circuits. You can use either 5Y3 or 5U4 for the R12R, or you could use my favorite, 5AR4. Whichever tube you chose should be put in the 5Y3 socket and build the power supply from that socket. Don't use the 5U4 socket. To see why I say that, look closely at the schematic in the area of the PT and rectifier sockets.

You only have a 12V filament winding so you must wire the tubes filaments in series just like the 6L6s are now. They will be wired in series pairs, ie, the two 6SN7s must be paired and wired in series and the 6SL7s must be paired and wired in series. You cannot pair a 6SN7 with a 6SL7 because they have different current requirements. This will be easy with the R12R. Could be a challenge or even impossible with your plan 2. I can't say without seeing a working schematic.

This project will be considerably more complex than that simple conversion you did last month. Just take your time. Get it right on paper before ever going to the bench.

[1blueheron]

 Sluckey,

I assume if building the R12R, the OA3 would be deleted along with the 5Y3.  Is there any reason to keep it other than it being a really cool tube to look at when lit.  I understand it is a voltage regulator?  Would it sound better if left in?

I have 2 output transformers.  Keep both or use one?

[sluckey]

Hmm, does the R12R have a 0A3??? That 0A3 is used to supply 75V to some external circuit. It is not used by anything on the schematic you posted. If you think it's cool, then just wire it in to the power supply for the R12R. It won't hurt anything.

The R12R only has one OT. The little one is paired with two 12V6s so it would work fine with two 6V6s for a small (probably 8 to 10 watt) amp. The big one is paired with two 6L6s and will probably produce 20 to 30 watts. I would use the big one and use the 6L6s in the R12R.

[1blueheron]

Hmm, does the R12R have a 0A3??? That 0A3 is used to supply 75V to some external circuit. It is not used by anything on the schematic you posted. If you think it's cool, then just wire it in to the power supply for the R12R. It won't hurt anything.

The R12R only has one OT. The little one is paired with two 12V6s so it would work fine with two 6V6s for a small (probably 8 to 10 watt) amp. The big one is paired with two 6L6s and will probably produce 20 to 30 watts. I would use the big one and use the 6L6s in the R12R.

Yes.  The old Conn has the OA3, none on the R12R.  I have no desire to keep a useless tube in the design. I will remove it.

I understand what you are saying about the 12V6 vs 6L6, however, at this point we are looking for something that can get some tube breakup before our ears bleed.  The 6V6 version of the R12R seemed to have a little more dirt and crunch at lower levels from what I understand than it's 6L6 or 7591 versions which were known for being clean.  What if I used (4)12V6's with the bigger transformer rather than the 6L6's and made a 2 tube cutout switch or just removed half the quad when we want less power?  Would the bigger transformer be a complete mismatch for the 12V6's? 

[shooter]

The 6V6 version

fwiw, I did a repair/Mod for a customer on a SET, one side was blown, OT, Pa tubes (7591's).  The customer wanted me to do that side as a 6V6.  He liked it better than the stock 7591's, but it's all subjective 
anyway, here's the basic PA 6V6 section, might have tweaked it after I drew it 

[sluckey]

I don't think you will ever find your bedroom crunchy amp while looking at high powered clean organ amps. Even a 6V6 Ampeg will be loud when it starts to break up. A better direction might be to sell that Conn and buy a used Epiphone Valve Junior to use as a baseline. You'll also be able to get your wife a nice Christmas present with the extra money from the sales of the Conn.

[shooter]

Even a 6V6 Ampeg will be loud

Yup, I really couldn't "test drive" the SET til the wife went shopping 
It wasn't twin stupid loud, but my neighbors definitely knew how bad a guitar player I am 

[SoundmasterG]

I understand what you are saying about the 12V6 vs 6L6, however, at this point we are looking for something that can get some tube breakup before our ears bleed.  The 6V6 version of the R12R seemed to have a little more dirt and crunch at lower levels from what I understand than it's 6L6 or 7591 versions which were known for being clean. 

Any amp design can be modified to produce breakup at whatever volume you want. Adding Power Scaling or similar would be the easiest way. If you didn't want to do that, you can modify the character of the preamp and phase inverter and the breakup conditions by changing the gain structure of the preamp and/or phase inverter so that any power tube can be overdriven. Ampeg was pretty conservative with their designs and the 7591 models they made don't breakup as much as the 6V6 models, but that is all in the design of the amp. It can be modified to do what you want no matter what power tube you use within reason. You still need whatever power tubes you use to match up with the characteristics of the output transformer and the voltages used in the amp.

Greg

[1blueheron]

I don't think you will ever find your bedroom crunchy amp while looking at high powered clean organ amps. Even a 6V6 Ampeg will be loud when it starts to break up. A better direction might be to sell that Conn and buy a used Epiphone Valve Junior to use as a baseline. You'll also be able to get your wife a nice Christmas present with the extra money from the sales of the Conn.

I guess I could sell the Conn and buy something but then the solder iron therapy is lost.  I am enjoying hunting these things down playing with them, and learning how they work.  I secured one Baldwin Orgasonic todaythat I will pick it up next week, and have a line on another.  It's a little addictive.  Is there a "valve addiction anonymous" group?  I might need to join.  Wife is threatening to leave if she doesn't get her kitchen table back this weekend...

I'll get started on doing some chassis layout diagrams and draw it up like the R12 R with 6L6's and bigger OT for now.

Soundmaster, that Power Scaling sounds interesting.  A quick Google led to London Power's power scaling kits.  Is that what you are talking about?  Please tell more.

[sluckey]

My idea about the Valve Junior was to buy a used one for the purpose of converting, modifying, experimenting, and just learning how these things work. It's a simple and affordable two tube amp that is very popular with modders and tinkerers. Lot's of info on the net. Might just be that bedroom/practice amp you have been wanting. This amp is simple enough that you could easily understand how it works and gain some valuable knowledge and experience working with schematics and layouts and troubleshooting. Kinda like building a Fender Champ. Take a look on eBay...

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR3.TRC1.A0.H0.XEpiphone+Valve+Junior.TRS0&_nkw=Epiphone+Valve+Junior&_sacat=0

Here's one that has been modified with an eyelet board. Lot's of valuable experience gained by doing a project like this...

https://www.ebay.com/itm/Epiphone-model-Valve-Junior-Head-modified-Tube-Audio/202498122335?epid=78605251&hash=item2f25d4225f:g:U9UAAOSwi3ta-bvV:rk:14:pf:0

I highly recommend a project like this is for anyone with no electronics training or experience. Take small steps. Learn and have fun too. Just might prepare you to tackle a bigger project such as that Conn.

===================================
Read this thread for info about power scaling aka VVR...

https://el34world.com/Forum/index.php?topic=6899.0

[SoundmasterG]

Soundmaster, that Power Scaling sounds interesting.  A quick Google led to London Power's power scaling kits.  Is that what you are talking about?  Please tell more.

Yes Power Scaling is London Power and Kevin O' Connor (KOC). I've put it on a couple amps and once  you get it dialed in it works really well and makes any amp usable at any volume level from bedroom level crunch to its max power level. It requires a master volume in order to work correctly as when you dial down the power amp, the preamp has to be dialed down in proportion but its a great product. If you buy it then it comes with free technical support from KOC so if you got stuck dialing it in the way you want he's available to help.


Greg

[sluckey]

Power scaling or VVR is something you may want to try on your "functional" Webster conversion amp. Plenty of room in that chassis.

[plumcrazyfx]

I'd like to see what this can become.  I have the same chassis.

[frankenxtein]

I have transformers that look similar to these  k-58054-2 (30:1) 7200 x 8 ohm 2.18 lbs , k-58459 606113 (32:1) 8k x 8 ohm 1.18 lbs , my method might not be real accurate the weights are with a luggage scale. The PT I have is k59841 1386113 , didn't mess with that one  14.5 lbs lol

[1blueheron]

Thanks to all who have provided feedback on this and for the suggestions, links and information.  It has given me a lot to think about and it caused me to take a step back, slow down and move a little more slowly. I am not going to abandon the Conn/R12R conversion project but I am going to delay it for a little while and move back to the Webster.  I had a small breakthrough on the Webster today... Updating the Webster thread.

So my plan right now is...

Put the Conn on temporary hold

Fine tune the Webster and perhaps VVR or power scaling for it

Build, or buy/modify a simple 2 valve amp and get a better grasp of design principles... Looking at VJR or 5E1 as potential candidates, maybe recycle the Eico 377 chassis for this?

Cancel the Mini Mace project for now.

Will post layouts for each project as I develop them.

[1blueheron]

In the process of working on schematics for the conversion project, I ran across this thread https://el34world.com/Forum/index.php?topic=22267.msg237342;topicseen#msg237342

It looks very close to what I have in mind.  Nice schematic and board layout.  I think I can adapt it to my project.

On the other front, I might have a line on a simple, SE tube amp.  Just found out my BIL is going through his storage room and getting rid of stuff.  He has an old Airline Bobkat guitar and "an amp that went with it".  Waiting to find out what kind of amp "went with it"....  Might be interesting.