First amp build

[Mongrel714]

Hello all,
 Try this again, I am building my first amp, I'm using the chassis from a Hammond organ, An AO-37, not a prime amp to convert, but I have cut down the chassis, and re arranged the components, I'm ordering some parts and getting ready to solder, I look forward to learning this craft, please take a look and see if I'm going in the right direction as far as wiring and parts, Ill have al new components except for the transformers, any parts that are on there now are place holders! Thanks in advance!

[Mongrel714]

Ok cool, I have seen the "Go her first" page so I will be looking through that as I go along, Thanks again!

[Mongrel714]

Hey guys, I do have a question here, The way the Heater twisted pairs are running, and the Blue and red from the Output tranny, with that as it is will the wires to the speaker jacks be ok were they are? in general will all the wiring be ok how it is run?? Thank you!!

[acheld]

Your heater wires are nicely twisted.  The priority is to keep your signal wires away from your AC (heater and mains) wires -- that's where you will have real problems.   

Avoid running your output wiring in parallel with AC.  If you need to run output wires across heaters, which most designs will do, cross at or near 90 degrees and separate in the Z dimension, just like Leo did back in the day.   

Don't get stuck on the wiring at this stage.   Do understand that this is a learning process, and have fun with it. 

You should have a plan drawn out.  Much easier to erase pencil lines than desolder wires and re-drill holes!   

For a first amp, I always favor Doug Hoffman's plans -- go to https://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&thispage=PartsListIndex.htm&ORDER_ID=!ORDERID!#google_vignette to find an amp similar to your design, and then check out the project links on the right, which will give you some ideas.

[dogburn]

If this was my project, I'd relocate the output transformer closer to the middle of the chassis, so that the wires could be run in more of a straight line to the power tubes and output jacks. That hole you have near V2 and V3 would be where I'd put it.

By the way, what amp model are you aiming to build? Looks like a push-pull of some sort. Knowing that would help people give you advice.

[sluckey]

I believe your OT is wired wrong. That OT has three primary wires. Blue and Brown should go to the output tube plates and red (center tap) should go to B+.

I agree with dogburn. That OT is located in a bad place. I suggest putting it between the rectifier socket and the output sockets. That will simplify those long wiring runs and the problems they may cause.

[Mongrel714]

acheld and Dogburn, and sluckey, Thank you for the reply's!
What I was hoping to build is a JCM 800 type 50w circuit, I don't know yet if the transformer is the proper voltage, The circuit I'm looking at is posted below,
I have been debating on moving the output transformer, so now Ill do that, and the signal wire advice will be taken acheld!
and sluckey, thank you for noticing that, I will correct that, mentioning the rectifier socket, using the diagram below, should I use the tube rectifier, or go with a Solid state rectifier here? I have already ordered a components kit with all the smaller resisters and caps, diodes, so whichever I should use would be fine with me!
 The turret board I'm using is 10" long so its a little cramped but should work, will there be a problem running anything under it given enough clearance?
I installed the proper fuse holder next to the power inlet, I have another on the way for the H.T. Thanks again guys!
Pics!



 

[Mongrel714]

From the output Tranny green and yellow wires to the speaker jacks, will the center tap (Black wire) go to ground?
THX!
Phones dead, Ill post the pic tomorrow!

[Rontone]

Are you planning on a set of EL34's in there?

I think those Hammond AO 20936-5 output transformers are for a pair of 6V6, not sure if one of the green and yellow wires may be for a specific feedback loop for that type of organ it came from [see this post on Hammond S6 from this forum]

https://el34world.com/Forum/index.php?topic=28335.0

The output transformers secondary wiring should be black to ground and green to hot on the output jack socket for 8 ohms, then the yellow is for a loop

I would recommend doing a JCM800 with 6V6 pair, 15w is plenty for home playing, I'm rocking a 2w JCM micro at the moment and its awesome!

Have a good read through these pages:- 

https://www.sluckeyamps.com/6v6plexi/6v6plexi.htm

https://mhuss.com/Plexi6V6/


It would be worth researching the transformers first, testing the mains transformer to get the power specs [which should be good for 2x 6V6 and a few preamp tubes]

Good to check the measurements from the output transformer, DC resistance measurements on the black green and yellow wires can help identify which order they go in, but a test with a small amount of AC into the transformer will help even more to get an accurate measurement of the ratios

Don't get stuck on the wiring at this stage.   Do understand that this is a learning process, and have fun with it.

Take your time with the base layer of the amp, sometimes it feels like the most boring bit, just drilling holes and endless filing but it is the foundation it all sits on....

[dogburn]

For your question on rectification, I would stick with solid state, since that was part of the Marshall design. If you switch to a tube rectifier, you would have to re-think the filter/reservoir caps to make sure they are appropriate for the rectifier and you'd have to make sure the power transformer can provide enough current for the 5V heaters of the rectifier.

[Mongrel714]

Hey guys, Thank you, this is the information Im needing, I am a noob at this so any info  you guys can give me is greatly appreciated! Rontone, There is a lot of great info in these posts, I've read and will re read it several times.
 The amp originally was running 6BQ5 tubes, (EL84's?) and the amp did work, you could hit the power button and jam out on some organ music! But I'm a guitar player soooo..The amp will spend the rest of its life amplifying guitars!
I've been watching Kley de Jongs videos to kind of get my footing here on where the hookups should be made, mainly this one:

it show a lot of the hookups he has made, but I will be concentrating on the pages you've sent me now to figure this out, the DC resistance on the OT is as follows:
Primary
Brown-Red:.102K
Blue-Red: .1127K
Brown-Blue- .219K
Secondary
Yellow-Black:0.2 ohms
Black-Green: 0.2 ohms
Yellow-Green: 0.4ohms
I have to de solder the leads on the PT to get the Resistance on it,
and I will be working on the VAC testing this evening to see what its putting out.

Thank you dogburn, I will be removing the Rectifier tube socket as my parts will be arriving on Mon. by the way the rec tube was a 5U4GC if that info is needed.
And gentleman, I am having a blast doing this, I have wanted to build a guitar amp for a very long time now, since I was on the road in the 80's Hair Metal craze!
Back then I ran through a JCM 800 100 watt, Traded that for a 100W early 60's Plexi, and the last road band I was in I ran two early 60's 50W Marshall heads with a double stack, nothing like standing in front of 16-12" speakers and feeling the air move! But I digress,
Thanks again guys, you dont know how much I appreciste the help!

[Mongrel714]

And by the way, I did move the OT guys,

[sluckey]

...the DC resistance on the OT is as follows:
Primary
Brown-Red:.102K
Blue-Red: .1127K
Brown-Blue- .219K

This confirms my earlier comment that the OT was wired wrong. Do not connect the red wire to a output tube socket!

I believe your OT is wired wrong. That OT has three primary wires. Blue and Brown should go to the output tube plates and red (center tap) should go to B+.

Another thing... Those transformers are designed for 6BQ5s or 6V6s. They will not be happy trying to work with EL34s!

And one more thing... The JCM800 2204 is a high gain amp. It will be very picky about layout. Your layout is far from optimized for a 2204.

BTW, the new location for the OT is much better.

[Mongrel714]

Thanks sluckey, I always aim a little to high, So Ill get measurements from the PT and well go from there.
I can live with a lower wattage, I'm not playing out now anyway, I just want to make something that sounds good and learn along the way!
and yes, the old setup used 6BQ5 tubes, (Those are equivalent to EL84's?) but since I have the Octal sockets installed I would rather go for the 6V6!

[Mongrel714]

Hey guys, I have all the leads from the PT un hooked, Can I Check each set of leads by hooking up the multi meter and pluging the cord in? Forgive me if this is a dumb question as I have not done this, but I will search now and see what comes up!
Well everything I've read says not to do this, so I'll wait and see what you guys say!

[Mongrel714]

OK as far as PT resistance we have:
Red to red HV: 92.7ohms
Red to Red/yellow CT: 47.6 ohms
red to red/yellow CT: 45.1 ohms
Yellow to yellow: 0.2 ohms
Large brown vinyl
to Large brown Vinyl: 0.2ohms
LBV to Grey CT:0.2 ohms
LBV to Grey CT: 0.2 ohms
Braided orange to
braided orange: 19.4 ohms
Black to black: 1.9 ohms
No continuity to any other lead, no continuity to ground.

[Rontone]

I did a search to check the AO-37's original setup, saw your reply on 18watt forum, so was this amp from a F100 Extravoice Organ?

With this schematic? [page 24 for Power Supply and Power Amp] - https://archive.org/details/HammondOrganF-100ExtravoiceServiceManual/page/n24/mode/1up

I was just wondering what those other taps on the power transformer were for

[Mongrel714]

Yes that's the one, It had a bank of 10-12AU7s with small transformers I assume for the "Extravoice" ? Maybe that was the 25V tap, (the two braided orange wires), the 5V to the rectifier socket (yellow), two large brown pvc are 6.3V,  two red are B+ to rectifier socket, red and yellow CT ran to B- terminal, (Will that run to the center tap B+ on the PT?) Two black to power switch/fuse, Here's some pics that may or may not help!
The PT was in a separate small enclosure on the bottom with a terminal strip on the outside.
This is that strip, on the prior pic it runs top to bottom, switch end at top. It also had a separate socket maybe a test plug socket?

[dogburn]

That's got to be a pretty massive PT, and it will certainly have the current to run all the tubes you have planned. Since it used a 5U4, the 5V tap should be rated for at least 3A.

Looking back at your photos, it looks like the amp model is AO-27, not 37.

[Mongrel714]

It would be worth researching the transformers first, testing the mains transformer to get the power specs [which should be good for 2x 6V6 and a few preamp tubes]

Good to check the measurements from the output transformer, DC resistance measurements on the black green and yellow wires can help identify which order they go in, but a test with a small amount of AC into the transformer will help even more to get an accurate measurement of the ratios

Ok, Im going with the 6V6 version, On the OT, do I need a variac, or is there another way to apply power to these, all the plug in power supplies I have including a 12V laptop power supply switch the power to DC. Ill research this see if I can find out what to use.

[AlNewman]

I think I have the same PT.  There was like 20 preamp tubes in the schematic I have, and 2 6V6 so you'll likely have quite high plate voltage.  Probably somewhere between 400-450V.  Mine reads 474 unloaded.
You will have to knock down the heater voltage with some series resistors, the heater winding is built for a lot of current to bring the voltage down to 6.3V.

[Mongrel714]

I think I have the same PT.  There was like 20 preamp tubes in the schematic I have, and 2 6V6 so you'll likely have quite high plate voltage.  Probably somewhere between 400-450V.  Mine reads 474 unloaded.
You will have to knock down the heater voltage with some series resistors, the heater winding is built for a lot of current to bring the voltage down to 6.3V.

Ah thank you Al, I was kinda wondering about that being so many 12AU7s!! Ive got enough sockets to last awhile!

[AlNewman]

Yeah, you're smart to change to 6v6 over el84's.  The PT could handle el34's or 6l6's easily, but the OT kind of confines you to the smaller wattage model.  That being said, you'll have to also adjust your signal voltage to work with the smaller output tubes compared to the 2204 schematic.
Personally I'm holding on to that transformer for some sort of stereo audio amp, but it comes in handy now for testing other circuits.

[Mongrel714]

Yeah, you're smart to change to 6v6 over el84's.  The PT could handle el34's or 6l6's easily, but the OT kind of confines you to the smaller wattage model.  That being said, you'll have to also adjust your signal voltage to work with the smaller output tubes compared to the 2204 schematic.
Personally I'm holding on to that transformer for some sort of stereo audio amp, but it comes in handy now for testing other circuits.

Thanks again Al, At the moment Im trying to figure out how to check the output on the Power Transformer, was watching one guy use a lightbulb current limiter to test the individual taps, I know the big brown tap is 6.3V, The yellow should be 5V, the orange colored is 25V, The B+ circuit is kind of what Im trying to find out, not very comfortable with this procedure though, just dont want to blow up my transformer!

[Mongrel714]

Ok, Finally got the guts up to test voltage, On the OT I have
120VAC in on primary blue and brown wires= secondary Green and black wire=1.3 V
"" ""  ""  "" ""  """ """ """ "" ""  "" "" = Secondary Yellow and black wires=1.3V

On the PT we have:
120 VAC in on black wires= 2 orange wires=28.8V output
                                         2 yellow wires= 5.3V output
                                        2 B Brown wires=7.3V output (You were right Al)
                                         2 Red HV to Red/yellow CT=336V output
So to figure ratios, Divide input by output, but on the OT Gr Bl,,Yel/bl do you use 1.3 V or add the two together and use 2.6V?
Thanks for the help all!!

[AlNewman]

Yes, a light bulb limiter is a good idea.  Plugging into a GFI is also a good idea.

On mine, there's the 2 big brown wires, that are the heater supply.  There's also a smaller green wire which is the heater center tap.  The black wires are the primaries. 
There's 5 red/orange wires.  The smaller 2 are the bias supply, the larger 3 are the high voltage. 
You can measure resistance across the 3 HV wires and find which one is the center tap.  Mine is 80R across both, and 40R/side.

You can test all of this with the amp unplugged.  Don't test voltages unless you're sure of what you're doing.

Then you can plug in and measure voltage from each HV winding to the HV center tap.  Should be around 330V AC.

[AlNewman]

secondary Green and black wire=1.3 V
"" ""  ""  "" ""  """ """ """ "" ""  "" "" = Secondary Yellow and black wires=1.3V

Not sure I understand this, your PT must be different than mine.

[Mongrel714]

secondary Green and black wire=1.3 V
"" ""  ""  "" ""  """ """ """ "" ""  "" "" = Secondary Yellow and black wires=1.3V

Not sure I understand this, your PT must be different than mine.

On the Output transformer, I input 120VAC into the primary Blue and brown wires, I measured 1.3V output from the secondary yellow/Black wires, and the green/black wires for 2.6V.

[AlNewman]

I thought you were talking power transformer.  No idea of your OT.

[AlNewman]

Uncle Doug has a good video on finding the ratio and impedance of the OT.

[Mongrel714]

Uncle Doug has a good video on finding the ratio and impedance of the OT.

Was just watching that one, lots of info!

[Mongrel714]

That's got to be a pretty massive PT, and it will certainly have the current to run all the tubes you have planned. Since it used a 5U4, the 5V tap should be rated for at least 3A.

Looking back at your photos, it looks like the amp model is AO-27, not 37.

Naw, its AO-37, The chassis was so long I cut it in half! I got some goodys in, this was for JCM 800 build, but Im sure we can use some for the 6V6!

[Mongrel714]

Hey Guys, I have been thinking about it and I really want to build the 50watt JCM, I'm getting a new 50 watt OT for my Birthday later this month, I'm building a Marshall correct chassis, (we have a metal break and whole metal shop, wood shop, graphics shop, were I work! I already have the amp head cabinet 70% finished, the electronics package is for the JCM 800, so here we go!!

[JPK]

I'm not crazy about the bias power supply switching off with the Standby switch. Should be powered in Standby like the heaters. There are better layouts out there as was mentioned. I attached the last 50 watt I assembled. Bias power is not switched off in Standby.

acheld and Dogburn, and sluckey, Thank you for the reply's!
What I was hoping to build is a JCM 800 type 50w circuit, I don't know yet if the transformer is the proper voltage, The circuit I'm looking at is posted below,
I have been debating on moving the output transformer, so now Ill do that, and the signal wire advice will be taken acheld!
and sluckey, thank you for noticing that, I will correct that, mentioning the rectifier socket, using the diagram below, should I use the tube rectifier, or go with a Solid state rectifier here? I have already ordered a components kit with all the smaller resisters and caps, diodes, so whichever I should use would be fine with me!
 The turret board I'm using is 10" long so its a little cramped but should work, will there be a problem running anything under it given enough clearance?
I installed the proper fuse holder next to the power inlet, I have another on the way for the H.T. Thanks again guys!
Pics!

[Mongrel714]

Thanks for the input JPK, I have totally shelved that mess, I have a new chassis built and starting to assemble, Taking my time with it, Wanting this to be closer to JCM 800 2204 style, please keep the comments and help coming, I need it!

[Rontone]

I'm not crazy about the bias power supply switching off with the Standby switch.

Yeah, and the fusing on the Secondary HT can be better, have a look at some standby and fusing ideas here:-

https://www.valvewizard.co.uk/standby.html

https://www.valvewizard.co.uk/fuses.html

[Mongrel714]

Bias switching off with standby, does that mean the tubes are un biased when the standby is on? What effect does this have?

[JPK]

Bias switching off with standby, does that mean the tubes are un biased when the standby is on? What effect does this have?

See post #13.
https://el34world.com/Forum/index.php?topic=23011.0

[Mongrel714]

I'm not crazy about the bias power supply switching off with the Standby switch.

Yeah, and the fusing on the Secondary HT can be better, have a look at some standby and fusing ideas here:-

https://www.valvewizard.co.uk/standby.html

https://www.valvewizard.co.uk/fuses.html

That makes sense, I wondered why my current amp had a couple fuses inside, now I know, still a little confused as to the location of the fuse to protect the PT, I'll re read that a few times till it sinks in my thick skull, I remember nights on the road and blowing a fuse in my Plexi, "give me some aluminum foil!!" Sometimes it would get me through the night, other times It didn't!! Anyways, thanks guys! Keep the knowledge coming!

[Mongrel714]

Neither layout in this thread gets the standby switch correct to the schematic they're noted to be based on.
Both disable the bias supply whilst in standby mode, thereby causing an enormous cathode current surge when standby is flipped.
Because the bias supply takes much longer to charge up than the anode and screen grid HT supply nodes.
Ok, got it!

[Mongrel714]

I'm not crazy about the bias power supply switching off with the Standby switch.

Yeah, and the fusing on the Secondary HT can be better, have a look at some standby and fusing ideas here:-

https://www.valvewizard.co.uk/standby.html

https://www.valvewizard.co.uk/fuses.html

Will this work? if not which way should I go??