Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on March 14, 2012, 12:09:38 am
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Well it begins! Does anybody have any info that this project has actually been built? I couldn't find any! but I was looking for an instance to see if the results was a good outcome. Some things about this amp seem kind of radical to my conservative fender background regarding tone stack, PI, NFB and power supply. So it's suppose to be a reverse engineered CG but you can't prove it by me. So I've started gutting the Baldwin amp and thinking how I will arrange things in there to make it fit. So attached is the Phoenix Project schematic and Layout that I will go by except I will be doing an old style P to P in my small chassis(no board). Platefire
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I'm referencing this link because this tread for the Baldwin Amp conversion actually started on the "Dr Z Carmen Ghia schems needed" thread. So some very good starter information for this project is listed there. Platefire
http://www.el34world.com/Forum/index.php?topic=13242.0 (http://www.el34world.com/Forum/index.php?topic=13242.0)
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From Dr. Z himself, here in his own words of an interview how the Carmen Ghia came to be:
Was that truly your first amp?
Not really. The Carmen Ghia was the first amp that I ever sold. To this day, I’ve probably built more of those heads than any other—somewhere around 400. It wasn’t even called the Carmen Ghia at the time. I named all of the early amps after my children—my grandson Carmen for the Ghia, and the SRZ was named after my daughter Sheree Roses. The original configuration for the Carmen Ghia was based on a Hammond reverb amp. I have a friend named Charlie Jobe, and if you look on Jimmy Smith’s albums you’ll see him credited—he was the Hammond organ master in the U.S., and he was almost in his 90’s when I met him. His house was just filled with Hammond stuff, and one day I saw these little EL84 amps sitting on a shelf and I asked Charlie what they were. He said, “Oh, those are Hammond reverb amps—they weren’t very popular.” They were optional for a B100 and it would tie the input from one of the speakers and drive its own separate speaker through a reverb pan. I thought that would make a cool guitar amp, so I built a few, and I’d take them to guitar shows and sell every one I’d brought for around $350 each. Of course, all of the $1,000 amps that I’d brought would be carried back out at the end of the show because in those days, no one wanted to spend $1,000 on an amp at a vintage guitar show.
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OK, I finished gutting the Baldwin Chassis last night. Here are some shots of what it looks like now.
Genral overall plan to put a bolt on cover plate over those holes in the top of the chassis to cover that area. Locate the input jack/vol/tone in front opposite end of OT end in front of 12AX tube sockets. Pilot light, power switch and standby switch to go in front opposite side in front of existing rectifier socket. The chassis came out of the organ with a bolt on steel bottom plate. So I plan to use that and mount four amp feet on it. Rear of chassis would use the existing power cord hole for a new 3 conductor AC power cord, use existing fuse holder and I'll need to drill another hole for speaker output.
So it's a tight fit especially with all the extra Carmen Ghia power supply circuitry. I have two basic plans for the power supply that I'm trying to decide on as follows:
1-Remove the rectifier socket from it's present location and install it in the hole that use to be A.C. Power outlet to the organ between the PT and OT. That would free up that area where the rectifier now occupies to maybe build a small board to mount most of the power supply.
2-Leave the rectifier in present location. Install a 50uf/50uf/500V can cap in the A.C. Power hole between transformers and then string out the remaining power supply circuit on three seperate terminal strips located around the rectifier area.
Right now I favor plan #1. If you have good reasoning why it might not be a good idea to move the rectifier to that location, please let me know! Platefire
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what i would do personally, and bear in mind that i'm not the sharpest knife in the drawer; i'd use the the AC power hole for a can cap and leave the 5U4 where it is. i'd make use of 16mm pots for the front panel. drill all the holes before proceeding. along end of the chassis with the four holes, id use one plate to cover all four holes from the inside and mount term strips to the cover plate for some of the pre-amp circuitry.
happy rosin smoking... :-)
--DL
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I think your #2 plan is best, and is what DL said too.
I don't think putting a hot Rec. tube so close between the PT/OT and with restricted air flow is a good idea?
Brad :icon_biggrin:
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You guys really threw a monkey wrench in my spokes :think1:
I was about to pull the trigger on a parts order with plan #1---now you got me reconsidering but that's what I ask you to do! So I'll hold off ordering and think about it a little more. No problem with full size pots. I only need a vol and a tone. I even sketched out a full size 4" long board to fit where the existing rectifier is at. I couldn't get it all on the board, the last part of the power supply circuit for V1A would have to go on the existing front terminal strip.
Anyway thanks for taking a look at it and I'll re-look at it from your perspective. Platefire
BTW-I have a NOS two 40uf/400v can that plugs into an octal socket. If I were to use that can in the existing hole with an octal socket with loaded voltage running 320VDC--I'm wondering if it would hurt if I skimp from the schematic 50uf/500V?
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BTW-I have a NOS two 40uf/400v can that plugs into an octal socket. If I were to use that can in the existing hole with an octal socket with loaded voltage running 320VDC--I'm wondering if it would hurt if I skimp from the schematic 50uf/500V?
It runs in my mind that you should allow at least 20% for startup (unloaded) voltage, and more is better. But for petey's sake, don't take my word for it! :smiley:
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Well on the can cap, I went back and looked at it and its 450V--so that's a little better. I never seen one that fits into a octal socket before. My radio station tech friend gave me two of those. The only bad thing is someone could actually un-plug the filter caps--just like a tube.
I've looked over the situation in the chassis and I really don't have room for a 3 1/8" wide board in the area of the rectifier even if I moved it to the back hole--it would be to cramped up against the pilot light, power and standby switches. I could cut the board down to less than 3 1/8" inches wide but I think I've sketched out a pretty good plan to install the power supply on terminal strips.
I want to do a layout plan for the rest of the circuit now. Just want to be sure how everything will go before I order the parts. Platefire
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Sorry to come late to the discussion. I have built this circuit several times. They sound great- and I have used Hammond Organ donors or scratch builds for mine. Here are some pictures.
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Duh, forgot to add pictures.
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Did you go by the schematic I'm using? and I see you have an extra control knob. Carmen Ghia's usually have only two--vol/tone. Platefire
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m3moser,
That is one beautiful wood cab! Nice job! :bravo1:
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Yes, gorgeous cabinet m3moser!
For Platefire:
I've gotta second DL's suggestion. Stick the cap can between the transformers, in the AC Power hole. If it were my amp, I wouldn't use a plug-in filter can, if for no other reason than you'll probably never find a functioning replacement when it comes time to replace it. Forget the risk of being shocked by a charged and removed filter cap.
If you have more than 1.75-2" in that space, you can easily fit a modern can cap. If you don't have over 335v unloaded output from the PT, then a 475v-rated can will work fine. 50uF/500v is just a leftover from what the reverse-engineered original had; I'd bet you don't need a 500v rating.
Now that I had a chance to grok your original plan (outside the two scenarios), I agree that seems like the sensible way to go. Plate over the holes, and have input enter in the vicinity of where the original can caps were, so that they can go into the 12AX7's and on to the EL84's in a logical manner.
Looks like an exciting project!
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Thanks HBP. Well I did a full size sketch tonight pretty much to scale and found a place to make all connections and place all components. It will require 7 extra terminal strips. Those are 5 term terminal strips and some of them will have to be shortened to fit in the locations shown. My sketch is probably un-readable to anybody else except me. I just needed to prove to myself everything could be fitted. Attached is the sketch but you'll never be able to read it. Platefire
BTW-On the sketch, I see where I left one connection off---V1B plate pin #6 to .01 cap on terminal strip to PI.
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m3moser,
That is one of the most beautiful cabs I've seen! Remarkable job. I love it. Looks to be figured cherry with flamed maple. Nice choice.
Platefire, he set a pretty high bar for you to meet! :icon_biggrin:
With respect, Tubenit
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Well it's kinda like Clint Eastwood said, Good to know your Limitations! :l2: In my case it's "Outer Limits" :BangHead:
BTW-I agree, fine looking cab! Now how about the gut shot!
This amp is a real brain teaser. I should of never gave my customer an option to convert or new scratch build. Live and learn! That's the amp I was planning a Stout for myself.
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Plate:
I didn't check every component and connection, but I do like your overall plan: power/rectifier portion of the chassis blocked off by filter caps, with terminal strips framing the sockets. I am using almost the exact same approach in my current build.
Looks like a winner!
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Good! Tight fit but unless I overlooked anything---should be good to go.
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that is a great drawing. good work!
i like to do this too before i start building. now i'm working on a B15 where i didn't draw the layout, only the board and it doesn't have the whole circuit on it. even for a 'simple' amp like that it's quite hard to make a layout while building it.
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Thanks birt! but that's a pretty pitiful drawing even by my own standards but-being it was sketched pretty much to scale it did allow me to work out the puzzel of getting everything to fit. At least it's a plan I can follow to git R dun. I did several other previous sketches that made me realize those plans wouldn't work. Not sure what a B15 is but I hope your project turns out well. Platefire
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ampeg B15n, single channel version. preamp with vol, treble, bass and PP 6L6 cathode biased poweramp.
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> Not sure what a B15 is
(http://t0.gstatic.com/images?q=tbn:ANd9GcRl55kzm_7oxd38S3Xu0lrc8ep8cGkl_nNeAQ5SxmU8EGRV4Vqc9g)
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Got a bass playing friend that has requested me build him a bass amp. I've been at a loss because most bass players I know just use SS amps and I have no experiance with bass tube amps. That might be a consideration--has anybody ever use that pre section but used it to 4-6L6's? Platefire
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:hijack1: (by OP)
Got a bass playing friend that has requested me build him a bass amp. I've been at a loss because most bass players I know just use SS amps and I have no experiance with bass tube amps. That might be a consideration--has anybody ever use that pre section but used it to 4-6L6's? Platefire
Hmm... Lessee Plate....
Firemedic's most related post as an answer to your question: http://www.el34world.com/Forum/index.php?topic=13458.0 (http://www.el34world.com/Forum/index.php?topic=13458.0)
Others talking about building a bass amp:
http://www.el34world.com/Forum/index.php?topic=13324.0 (http://www.el34world.com/Forum/index.php?topic=13324.0)
http://www.el34world.com/Forum/index.php?topic=13001.0 (http://www.el34world.com/Forum/index.php?topic=13001.0)
:icon_biggrin:
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Well I'm getting parts in so it's time to start moving out on this CG clone.
I got a JJ can cap 50/50uf 500v 1 3/8" diameter with clamp. So I've never actually installed a new can cap before. The existing hole in chassis where I want to install the can is 1 1/8". It appears to me I could just butt the can up to the chassis hole and let the connectors stick through the hole and it would work that way. If I understood previous discussions about installing a can like this, the norm is to drill the hole out (1 3/8") so the can with stick through the chassis to the inside. Is that necessesary? Don't think I have any means on hand to drill out that big at the moment. Platefire
BTW-the hole between the transformers is where the cap needs to go.
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I prefer to have a smaller hole so the bottom of the cap can rest against the chassis. Here's some I replaced that's a similar case as yours...
(http://home.comcast.net/~seluckey/amps/hammond/h02.jpg)
(http://home.comcast.net/~seluckey/amps/hammond/h03.jpg)
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Thanks Sluckey! As they say, a picture is worth a thousand words. Nice layout and lead dress! I wish I had as much chassis space as you do to play with but I'll not complain and consider it a challenge.
One question though, I don't see any grounding wires going to the can cap ground lug--am I just not able to see it or what? Platefire
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Can you see'm now? Black wires connected to a star ground just to the right of the PT.
http://home.comcast.net/~seluckey/amps/hammond/closeup.jpg (http://home.comcast.net/~seluckey/amps/hammond/closeup.jpg)
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Can you see'm now?
No, I can't see them. Should have used pink colored wire? :laugh:
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Sho Nuff! See'm Now. At pictur is wurth bout 10000 wurds. sluckey I fishally Krown U a "redneck Kammunicator" at means U r Kapeable ov Kammunicaten wid a red neck widout a interpatur.
Corngradulasions!!!! I'll pass da wurd 2 da udder toob heds hear n Lousyana. :icon_biggrin:
Seriouly-Thanks! Platefire
BTW-Went by Lowes this afternoon and got a 22ga x 6" X 18" steel plate for $5.00 to make a cover for the top holes cover. I usually have some plate on hand to use in a case like this but my stock is running low. Also got a couple of plastic 3/8" plugs($1.07) to cover a couple of un-needed holes plus a package of #6 x 32 x 3/8" long machine screws ($1.26)and nuts to bolt down the plate/terminal strips. Simple little stuff is getting expensive these days!
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Sho Nuff! See'm Now. At pictur is wurth bout 10000 wurds. sluckey I fishally Krown U a "redneck Kammunicator" at means U r Kapeable ov Kammunicaten wid a red neck widout a interpatur.
Corngradulasions!!!! I'll pass da wurd 2 da udder toob heds hear n Lousyana. :icon_biggrin:
Dog Gone cajin's, don't know what their sayin, but I Love their music & food!!!!! I-eee!
Save me some of those crawydads!!!!!
:m2
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CORRECTION! Well a Red Neck is what is found in the Northern Hills of Louisiana, can be called by "Bubba" and incorperates two or three English words together into one like "airyago" interpreted "There you go". Cajuns are found in South Louisiana in the swamps/marshes and speak their own brand of French. Shoot Him! Shoot Him! interprted &^%)#@
OK back to the Carmen Ghia!
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Back to my previous Baldwin Output transformer test. The results were as follows:
I put my 14.44 VAC to the OT two primary brown and blue wires to plates and got .37 VAC measuring across the two secondarys/speaker wires.
14.44/0.37=39.03= That Means turns ratio 39:1
39 X 39=1521 turns ratio squared means impedance ratio of 1521:1
So in a given load impedance of 8 Ohms the transformer is 8 x 1521=12168 Ohm or 12.2K
I HAVE QUESTIONS:
1-Does the results of my test indicate the OT output is 12 Ohms??? or am I reading the results right?
2-What Ohm speaker needs to be used with this for best results??
3-My intent was to use 8 Ohm speaker--will this work?
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-Does the results of my test indicate the OT output is 12 Ohms??? or am I reading the results right?
I am only answering this because talking about things helps me learn them, not because I actually know. :laugh:
I think that the 12.2K impedance that you came up with means that it's a good match to use the 8 ohm speaker with 2 6v6/6L6 tubes. I think I remember PRR saying that a 6V6 "likes" about 6K. So with a P/P 2 tubes that would be about right. :dontknow:
Not only "could be" wrong, but "probably am" wrong.
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Well Thanks John. I've got PP/EL84's kinda similar to a 6V6. Yeah I just don't know how to feel about my OT as far as what Ohms it actually is and rather it would be a good match for my 8 Ohms speakers. Impedance and Ohms regarding OT is kinda like Voodo to me---don't understand it. So I was hoping somebody in the know could positively answer my questions in the previous post. Platefire
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Today I drilled the chassis and patched/covered the un-needed holes from gutting out process. Getting close to where I can start wiring it up. First I need to carefully place about 7 terminal strips.
It is starting to look more like an amp now.
Do you think I could get away without painting that unfinished 22 Ga steel cover plate I added or should I prime and paint it? Platefire
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I think, sooner or later, that steel is going to rust.
You could paint it with aluminum paint and it would sort of blend in.
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Or, you could clear coat the steel plate so it won't rust.
Looking good.
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Yeah I thought the patch plate matched the existing chassis pretty good as is and the chassis is un-finished steel. Clearcoat might be a good idea or just gray primer.
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I was thinking these Baldwin chassis might be a type of steel alloy like a stainless.
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mresistor
Your probably right or it would have already rusted up. At any rate I will pull the cover plate off and paint it because I do want to build my stuff to last. Platefire
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Back to my previous Baldwin Output transformer test. The results were as follows:
I put my 14.44 VAC to the OT two primary brown and blue wires to plates and got .37 VAC measuring across the two secondarys/speaker wires.
14.44/0.37=39.03= That Means turns ratio 39:1
39 X 39=1521 turns ratio squared means impedance ratio of 1521:1
So in a given load impedance of 8 Ohms the transformer is 8 x 1521=12168 Ohm or 12.2K
I HAVE QUESTIONS:
1-Does the results of my test indicate the OT output is 12 Ohms??? or am I reading the results right?
2-What Ohm speaker needs to be used with this for best results??
3-My intent was to use 8 Ohm speaker--will this work?
I've been thinking about this some more but didn't follow up cuz I thought someone else would. First, why did you think your test meant 12 ohms? The output impedance with an 8 ohm speaker is 12.2K ohms. If you had wanted to use a 16ohm speaker, your impedance would be 24.3K ohms. So if I'm understanding thing correctly, I might actually have been right.
Which explains the heavy storms out west.
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14.44/0.37=39.03= That Means turns ratio 39:1 OK
39 X 39=1521 turns ratio squared means impedance ratio of 1521:1 OK
So in a given load impedance of 8 Ohms the transformer is 8 x 1521=12168 Ohm or 12.2K OK
I HAVE QUESTIONS:
1-Does the results of my test indicate the OT output is 12 Ohms??? or am I reading the results right? No
2-What Ohm speaker needs to be used with this for best results?? 4Ω will reflect 6K to the tubes. Pretty good for EL84 or 6V6
3-My intent was to use 8 Ohm speaker--will this work? It will work. 4Ω is mo betta.
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Hay! Hay! Hay! Thanks-----Appreciate you clearing that up for me. Is there any chart or info page I can download as a reference that gives the K impedance required for a OT for each type of tube setup or is that provided in the tube specs?
Also what would the impedance need to have been to be best suited for a 8 Ohm speaker with PP/EL84? Sorry for asking all these dummy questions but I never got into this to deep before---but as you see it's very much needed. I've learned how to test the impedance of any given OT, I just don't know how to interpret the data once I get it! Platefire
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Is there any chart or info page I can download as a reference that gives the K impedance required for a OT for each type of tube setup or is that provided in the tube specs?
I've seen a chart that has most of the common output tubes with plate impedances but don't know where it is. Probably on this site. Do a search.
Also what would the impedance need to have been to be best suited for a 8 Ohm speaker with PP/EL84?
I'd say 8K:8Ω, or 6K:8Ω
Something you may need to nail down... An OT has no impedance itself. It simply matches the high impedance of the output tube plates to the low impedance of the speaker. When you see an OT spec that says 6600Ω:8Ω, you're really seeing a RATIO. Those numbers mean the OT would make a nice match between 6600Ω plates (think 6V6) and an 8Ω speaker. But it's a ratio and as such, 6600Ω:8Ω is the same as 3300Ω:4Ω, and those numbers make a nice match to 3300Ω plates (think 6L6 or EL34) and a 4Ω speaker. I'm not gonna say anything about power other than the obvious... Higher power tubes naturally want a higher power OT.
So, what happens when you use an OT that doesn't have the proper impedance ratio? This is an impedance mismatch and you cannot transfer all the power from the tube plates to the speaker.That's the main thing you need to know.
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Thanks sluckey
I don't have complete understanding yet but I now know about 100% more than I did. I did some searches on google last night. I've been reading OT specs. I have to say I'm a little confused about
dividing up the K impedance between SE, PP 2tube/4tube. For instance---looking at a Fender Replacement OT for a tweed deluxe indicates Primary impedance=8000CT/8 Ohms. I'm thinking two 6V6's at 8000K x 2=16000K/2 6V6's=8000K. Reason being I'm thinking of my existing 12.2K/2 EL84's=6.1K each that we just discussed.
Also looking at a Fender Blues Jr spec which I know is PP/EL84 Primary Imp. is 6950CT/8 Ohms--I assume the ratio you discussed. Still befuzzeled thinking of the combined impedance of two EL84 output tubes compared the the spec 6950???
I have learned that impedance is like a resistance and Ohms is the measurement of the impedance--from the anology of a water hose with water pressure being voltage and the amps increasing/or decreasing with the water pressure(voltage) and your thumb over the end of the hose holding back the pressure is impedance. I understand as you said the OT is a impedance matching device between high impedance tube plate output and low impedance speaker. At least I think thats what I understand?? Har! if that's correct?? :think1: Platefire
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two 8 ohm speakers in parallel would be cool...sound good too..
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I have to say I'm a little confused about dividing up the K impedance between SE, PP 2tube/4tube. For instance---looking at a Fender Replacement OT for a tweed deluxe indicates Primary impedance=8000CT/8 Ohms. I'm thinking two 6V6's at 8000K x 2=16000K/2 6V6's=8000K. Reason being I'm thinking of my existing 12.2K/2 EL84's=6.1K each that we just discussed.
It don't work like that.
But that's okay... Look at what you can find for "replacement OTs" for particular amps. Note the type and number of output tubes, and the spec primary impedance of the OT. You'll start to see typical pairings, although these can vary.
Also looking at a Fender Blues Jr spec which I know is PP/EL84 Primary Imp. is 6950CT/8 Ohms--I assume the ratio you discussed. Still befuzzeled thinking of the combined impedance of two EL84 output tubes compared the the spec 6950???
Well, 6950 is pretty much 7k. 7k is pretty dang close to 8k, at least closer than 3-4k is. So, let's call it "six of one, half-dozen of the other".
You're wanting to rebuild this amp into a Carmen Ghia. The original amp used this OT with a pair of EL84's. You have figured out on your own that the probable speaker load needs to be 4 ohms. I think your work is done.
If we live and die by each clean watt coming out of the speaker, we might need many copies of a set of plate curves, a mechanical pencil, and a lot of time spent trying various proposed plate loads.
But you and I probably won't know the difference between a 14w amp and a 25w amp, except by how high we have to turn up the volume knob before distortion. So laboring over the "perfect load" is probably good for later when you want to work a puzzle.
Instead, we need to know, "will it get up and go?" Kinda like buying a used boat, and considering replacing the motor. Do you slap on the whopping 22HP motor from a professional lawnmower? Or do you strap on a 470HP V8 tweaked for street racing? Probably not, unless you want to either sink with the engine off or turn boat into a really lousy paper airplane with it at full-rev.
Or maybe you pick a 115HP V4 motor similar to what it came with when you bought it. If you really wanted a step up, you might get a 130-150HP motor, not too different than what is already on it. Or, maybe you say, "runs good-enough. I'll leave what's on it."
Don't sweat it. You can leave what's on it. :icon_biggrin:
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Well It just isn't for this amp. Yeah we have determined a 8 Ohm speaker will work, a 4 Ohm mo-better! Since I was already into this OT learning curve--I was just trying to learn a little bit extra for future reference. My amp knowledge is basically just general at best--not to deep into any one thing but in this paticular area---output tubes to OT I've almost been less than general knowledge--so cut a ol country red neck some slack! It may take me a long time to "get it" but once I got it "I got it", for a day or two anyway! :icon_biggrin: Thanks, Platefire
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Hey HBP/sluckey
I didn't mean to run ya'll off! Like we say here in the South "I was just "funnen around".
I always appreciate your help and advice even if it comes in the form of a mild rebuke, as may be sometimes neccessary. You have my respect! So sometimes I say things jokingly because I'm a generally a happy camper---just wanted you to know I don't mean any disrespect by it. Platefire
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I ain't gone. Just don't have anything to say at the moment.
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No worries here... I'm southern too!
In any event, my post wasn't meant as a rebuke. All of us amp-heads tend to go through a phase where everything seems like it "just has to be critical, right?" Kind of like the amp blueprinting idea, where if you just use 1% resistors for everything, then you'll have a great-sounding amp. Or unless you use the exact same waxed fiberboard as Fender, your amp won't have that "mojo".
It's somewhat the same with OT's, within some degree of reason.
There is a theoretically "right" primary impedance for a particular tube, supply voltage, class of operation and desired clean output power. But because the speaker doesn't exhibit a constant impedance, the primary impedance will not be constant in practice. So to a limited extent, worrying about anything much tighter than maybe a 20% or so tolerance is maybe not worth the mental stress.
I think from what Sluckey helped you figure out 4 ohms of speaker load should be ideal for this OT and build. :icon_biggrin:
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Well the amps going to a customer. So I wanted to be able to tell him what would be the best match.
John came in and tried to help me on the Ohms and sluckey came in and nailed it. So maybe John and I both learned a little.
For the same customer I built a tweed deluxe type head about three years ago thats clearly marked 8 Ohm speaker on the back of the amp. What did he do, he went and bought a 16 Ohm cab to go with it and thinks it sounds great!!?? Go figure?? :dontknow: Platefire
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So maybe John and I both learned a little.
Heck yeah,that's why I jumped in!
Now if only I can remember it.
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Question??? I just hooked up my heater wiring to two 100 Ohm artifical taps to ground to the two Orange PT heater wires. Same as on the Baldwin circuit except they used two 50 Ohm resistors.
My question is I'm getting continuity with ground on both sides of the 100 Ohm resistor--with the ground side and the PT wire side. I was thinking it shouldn't be continuity on the PT side heater tap?
Is there something wrong here or is that normal? Platefire
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I'm getting continuity with ground on both sides of the 100 Ohm resistor--with the ground side and the PT wire side. I was thinking it shouldn't be continuity on the PT side heater tap?
Does the PT have the 6.3v heater wires grounded already making the artificial ground unnecessary?
With respect, Tubenit
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My question is I'm getting continuity with ground on both sides of the 100 Ohm resistor--with the ground side and the PT wire side. I was thinking it shouldn't be continuity on the PT side heater tap?
'Continuity' is kinda vague. Do you mean 0Ω, 50Ω, 100Ω, 1000Ω, etc???
The 6.3VAC winding is just a long piece of big wire. Wire resistance is probably only a couple ohms, maybe even less than one ohm. If you also have a real center tap connected to ground, then the resistance reading on both sides of the resistor to ground would be near zero (reading thru the winding). If no real centertap is connected, then the reading on one side of the resistor will be 50Ω and the other side of that resistor will be zero ohms. You could say the two resistors are connected in parallel by to long wire which is the secondary winding.
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sluckey
To my knowledge this PT has no heater CT. I carefully documented that the orange wires went to the heater wires grounded with two 50 Ohm resistors for artificial center taps in the original Baldwin circuit. I hooked the heater wires up the same way on the new circuit using 100 Ohm Metal oxide 1 watt resistors. On the new heater wiring/circuit with my MM set to Ohms, ground/black term connected to chassis and red/hot touching both sides of 100 Ohm resistors----I get "0" Ohms on grounded side of resistor and 50 Ohms on non-grounded side--just like you said.
When I say "Continuity", I'm using the continuity setting on my MM where you don't get a reading but a "Beep" when you have continuity. So I was saying that I was getting a "beep" on both ends(ground and heater tap) of my 100 Ohm resistors. This confused me a little because I was expecting continuity to chassis on the grounded side of the 100 Ohm only. Also when I connect my MM ground to chassis I get a continuity "Beep" with all heater wiring on tube pins(with no tube connected).
Just as a second check, I pulled the back off my DIY champ that has a PT CT instead of a artifical CT. On all the heater wiring tube pin connections I also got a continuity "beep" to chassis ground on both runs of heater wires going to each tube. So I'm assuming that having continuity "beep" to ground throughout all heater wiring is normal and at least that aspect of my hookup is correct??!! Yes? No? Thanks, Platefire
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Don't overthink this. Remember the KISS factor.
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I think what we have here is a senior moment because I've done this Bokoo times. At least that sounds like a good excuse. I use to just hook-um-up, move on and not think about it! :laugh:
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OK, Demo/Gutting Phase--Done
Chassis Prep Phase--Done
>>>>On to Circuit Build Stage!
The chassis is kind of hard to handle picking up and moving around, so I added some handles.
Added feet on the bottom plate. Platefire
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I've been wiring in the CG circuit. This old style point to point without a board is pretty tedious----give me a good turret board and plenty of chassis space any day! I sure hope everything works well when I get it done----I would sure hate to tear some of this tangled mess out. :sad2: Platefire
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I was just reading this Sunday, and wondering how you were doing with it. :smiley:
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Finishing the chassis metal.
Get some naval jelly, and rub it on the steel. The naval jelly contains phosphoric acid and converts the surface to iron phosphate. It won't rust and gives a nice dark finish. By the same token you can sign your work using naval jelly. then clear coat it.
Other places to get similar stuff is an auto body shop supply store.
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Got the power section, output stage and PI wired in. Just lack the input, tone stack and power cord.
I've been taking my time double checking everything along the way. I should have it ready for initial fire up by the end of the week. Platefire
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Finished wiring and fired it up today. It works but not good! Found two wiring mistakes---resistor in wrong location and one resistor value incorrect. My fault, but I really think this reverse engineered schematic is not all together correct. I got some really crazy stuff going on here that's kind of got me aggrivated. So I'm going to take a break from it and refresh myself before I resume. Platefire
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but I really think this reverse engineered schematic is not all together correct.
It's not. Comparing the Ghia schematic to the original AO-35 you'll notice there is a 25µF filter cap missing from node D on the B+ rail. This is the 24v supply for the fixed bias PI circuit. I bet that's an oversight on the drawing and I believe the Ghia really has that cap in place. Real easy to stick one in the circuit. All you need is a 25µF/50v cap. Bet it will sound much better. If this cap doesn't fix it post tube voltages as well as B+ rail voltages.
That PI is an unusual circuit and with the fixed bias supply to the grids and cathodes, it could be easy to make a wiring error too. So, just be careful and precise.
I've compared the two PI and power supply circuits. They are identical except for that missing filter cap. I've attached the orig AO-35 schematic for comparision just in case you don't have it...
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sluckey
I got a good nights rest and hit it again this morning. I had put R3 behind the R2 which should have been right behind R1 which cut the voltage on everything downstream plus R5 should have been 82K and I had it 8.2K. So that really had my voltages screwed up. I relocated R3 and the only 82K R I had on hand was a 1/2 watt, so I put it in there until I can get a 3 watt metal. WoW! when I did that all my voltage readings straightned out. I'm now within 1 to 7 volts difference at every point of distribution throughout the whole circuit. I couldn't of found a better match for a PT if I had tried for this circuit. It's sounding so much better. I don't know what a Carmen Ghia circuit is suppose to sound like but the things I've noticed is as follows:
1-Pretty bright circuit!
2-Tone control adds more bass clockwise and more treble counter clockwise??? backward than normal! I'm pretty sure I've got it wired like the schematic. I can get close to my tone at about 4:00 oclock and volume about 8:00 oclock.
3-Very little clean headroom. Circuit starts to get into pretty heavy breakup a 9:00 or 10:00 oclock on the volume and continually gets more distorted until the last 1/8 on volume and then goes into cut off. Good thing is the distortion had good harmonics :icon_biggrin: I used the 3.3 Meg feedback resitor. Might need to try the 2.2 meg for more headroom. That would be customers call. It will be used in a recording studio--he might like the early breakup.
I didn't add C10 that was marked optional. I'm wondering if I should add it? I had not caught the missing 25/50 cap at node D until you mentioned it! I've got to order R5, so I guess I could order that cap with it. All and all the amp sounds and responds pretty good. It's running pretty quiet too. Thanks, Platefire
BTW-Regarding the 25/50 bias cap, here is what is suppose to be a gut shot of the Carmen Ghia and there is no visable 25/50 cap accross the 8.2K resistor. What do you think?
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BTW-Regarding the 25/50 bias cap, here is what is suppose to be a gut shot of the Carmen Ghia and there is no visable 25/50 cap accross the 8.2K resistor. What do you think?
Here's another one and it does have the cap.
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I had to get the schematic out and study it awhile because the layouts and lead dress of the two pictures are so different--hard to believe both of them are Dr. Z's? So I finally figured out the big silver cap is the 25 uf on your pic. Well I've already put in an order with Doug and included a 25/50 with it. Do you think both pictures are Dr Z amps?
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I don't know if either of those amps were built by Dr. Z. I doubt they were built by the same person. I have both those pics in a folder for Carmen Ghia. I had searched for info on the CG several years ago but lost interest. I have some schematics called Pheonix and others called Botany Bay. They're both the same, but not exact copies. I never did find any info claiming to belong to Dr. Z.
My gut logic says the cap is needed. The lower grid on the PI needs to be at signal ground to function as Hammond designed. Don't know what effect omitting the cap will have. Could be part of the CG magic. But it's very easy to tell if you think it's necessary just by patching it in. You can clip it in and out while the amp is running and decide which way you like it better. Give us a report and let us know what you decide.
Maybe PRR or HBP will ring in with some circuit analysis theory.
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A little photo forensics first.
The photo that Platefire posted looks like what I believe is a Dr Z-made Carmen Ghia. I say that because the wiring and board mounting is just slightly better than the chassis in Sluckey's picture, and the chassis is yellowish. Dr Z used to (maybe they still do) use an aluminum chassis which was given a chromate dip; the chromate gives the chassis the yellowish look. Additionally, the red glyptal marking the turrets which have been completed is something Dr Z did (again, I don't know if they continue to do this).
So it looks like the chassis more-likely to be a Z doesn't have the cap (at least in this one example).
But Sluckey's right. This phase inverter (probably the one I'm least familiar with) is a differential amplifier, or basically a fixed-bias long-tail. There is one grid directly driven by the preamp signal, and normally a large-valued resistor over to the other grid, which then usually has a cap to ground. This circuit needs an input signal which represents a difference between the two grids, as a typical gain stage has an input which is a difference between the grid and cathode voltages. Most commonly, this is done by driving one grid while keeping the other at a.c. ground (via the cap), which then results in a difference between the two grids.
You might be tempted to think the resistor between grids makes both grids see the same signal. Assuming no current flows through the resistor, it really keeps both grids at the same d.c. voltage. The cap to ground then looks to signal like 0v, which you could think of as a voltage divider like a volume control turned to 0.
So with no cap, we have a divider made of 470k and 8.2k. Not the same as a.c. ground via the cap, but that keeps what in-phase signal which does leak to the "non-driven" grid relatively small.
I think all-in-all, losing the cap would make the phase inverter have less gain and output swing. The "right way" is to use the cap. I'd be curious to see how large the phase inverter output is with the cap, and whether it drives the EL84s to overload to easily. Maybe Dr Z wanted to hamstring the phase inverter just a little bit to have more range on the volume control.
The easy way is just to try the amp with and without the cap. If you anticipate building more than just this amp, you can probably find a use for extra 25uF/50v caps hanging around.
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Thanks sluckey and HBP
I tell you what, if I had enough room I would put the cap on a switch but I'm already very tight roomwise. I might could work it in with a midi switch SPST. When the part comes in I'll just try it out. I don't think I want to loose anymore headroom unless I can make it a switchable option. My customer is in Georgia, so he can't exactly drive over to the house and test. I'll have to make the right choice myself. Thanks a bunch for your help. I'll post the effect the cap has on the amp when my parts come in. I've been jamming on the amp and I'm liking it more and more. I think Randy is going to be happy with it. Platefire
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> regarding the 25/50 cap parallel to the 8.2K resistor to ground on the +24V to PI grid. .... needed or not?
Not needed. I do not know why Hammond has it. I suspect the design changed several times.
The "loss of gain" mentioned is valid... but in the ratio 470K/(470K+8K) or 0.98, truly insignificant.
The 8K does NOT have to be 3 Watt. Tenth-watt is fine, use 1/4W or 1/2W. (The 82K dissipates 0.66W, so a 1W won't live forever, 2W is safe, 3W seems to be common these days.)
BTW: on Hammond if you un-strap points 8 and 9 the PI goes dead fairly benignly. I suspect this was a remote mute so the organ could go dead silent yet be ready to play in a split second. Unlike the guitar-amp custom of de-powering all the plates, this leaves the power tubes cooking, but no signal can get through except the really inaudible hiss of the power tubes.
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Well Good and thanks PRR. That solves the riddle of the 25/50 cap. Meantime I've been working on other issues with this amp while waiting on the 82K 3 watt to arrive. I could use some help and would appreciate your input on these issues:
1-Got a very slight humm through the speaker on standby with the power on. Heater taps are grounded with two 100 Ohm artificial CT. I pulled the tubes, still there. My first thought was heater wires too close to OT plate wire. Moved those around with no change. I've moved heater wiring feed from PT in realation to any other close wires and no change. I've tried plugging it in at another room/outlet, no change. Heater voltage measured 6.65VAC under load. You can't hear this hum until you turn the TV off and all other stuff off but I don't have this on any of my other amps--- I think it shouldn't be.
Edit: #2 below was the preamp tube. A brand new EH. It will now go full blown gain with my GE vintage 12AX7.I had tried swapping all the other tubes except the V1.
2-When cranking the volume up on this amp it goes into complete cut off of sound/volume from 85% to 100% of volume. I've tried different tubes, moving wires around to get seperation and double checked component values/connections---no change. I know it will probably never be used at that volume level but---it shouldn't be cutting out.
3-Tone Stack. I've got it hooked up just like the shematic but counterclockwise increases treble and clockwise increases bass/lows. This is completly backwards from normal but it's wired like schematic!
Hope ya'll have some answers for this. Thanks, Platefire
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3-Tone Stack. I've got it hooked up just like the shematic but counterclockwise increases treble and clockwise increases bass/lows. This is completly backwards from normal but it's wired like schematic!
I did the same thing. You have to watch which side of the resistor symbol the <--- wiper symbol is on, I think it changes which side is the CW or CCW. Simple enough to change the components though.
Of course, if I could memorize (without looking it up) what makes a low-pass and high-pass filter, I wouldn't have that problem! :smiley: I need to buy a second Merlin book to keep on my bench.
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3-Tone Stack. I've got it hooked up just like the shematic but counterclockwise increases treble and clockwise increases bass/lows. This is completly backwards from normal but it's wired like schematic!
This looks like how the tone control works. The interior picture posted before also look like the control is wired as yours is wired.
Look back at the schematic you included in your first post. R24, R25, C16, C17 form a bridged-T filter; C11 is just a coupling cap into the circuit. You could look at C17 as rolling off highs by shunting them to ground, while C16 tends to cut lows and pass highs around the resistors and C17. So the circuit has both high-pass and low-pass parts, and mids are scooped out where the two cross-over.
When the tone control wiper is moved towards the "top" of the pot as drawn, the highs that had been preserved by C16 get shunted to ground through C17. When the wiper is moved towards ground, C17 is shunted which removes the frequency-dependent part of the low-pass filter; this leaves trebles dictated by C16.
I haven't played a Dr Z Carmen Ghia, but the photos posted seem to match your wiring. My best guess then is that the original amp also has a tone control which seems "backwards".
I did the same thing. You have to watch which side of the resistor symbol the <--- wiper symbol is on, I think it changes which side is the CW or CCW.
That would be helpful, but isn't the case. Some schematics will place small symbols by the "resistor" of the pot, to indicate which end is the clockwise and counterclockwise ends. Interestingly, the diagonal arrow through the "resistor" of a pot wired as a rheostat might indicate which end is which, but I can never remember how that works.
If the tone control operation bothers you, you could swap which ends everything is wired to. But at least you should know that you're wired correctly according to your schematic.
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Thanks HotBluePlates
Good explination on how the tone stack works. I really good with the way it works as far a movment of the knob. With one tone knob it's a no brainer. You turn it to you get the sound you like. For my purposes about 3:00 to 4:00 Oclock is my tone.
Since I've learned the cut off problem was the preamp tube I've expermented with several tubes for best sound and the Baldwin 12AX7 that came in it sounds best so far. I wonder who made those for Baldwin?
I guess there isn't any explination for the low volume hum through the speaker from just AC unloaded operation. I was really trying to get the noise down low as possible because this will be a recording studio amp. I guess he can do what I do and use a noise gate on the amp mic. Downward Expansion works best for me on that.
On hind site I guess we can now confirm that the Phoenix schematic is pretty much right for the Dr. Z Carmen Ghia! We've gone over it pretty thoroughly. Only mistake I found is voltage reading to PI 330K plate resistors at 235V. If you look down in the power supply section at point "C", you see the voltage is 290V which is correct and should be 290V before the 330K resistors. The 235V is correct for the plate voltages on the PI after the 330K resistors.
Thanks a bunch!!! Platefire
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That would be helpful, but isn't the case.
Well dang. And here I thought I was so smart. :laugh:
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Hi John
Well I didn't even know some pots have symbols to show the movement---first time I heard that!
So I will probably tell the customer how it works and if he has heartburn with that, I can wire the tone pot backwards from the schematic.
One thing weird I've noticed about this tone stack is even when you have it set on the dark side there is a treble peak or bell tone that breaks through the underlying lows. So even though you may have you neck pickup set for jazz tone when you pick it's going to cut through. This is just jamming by myself, I haven't tried this with a band yet--where the rubber meets the road.
Both extreams settings of the tone stack are unusable---treble way hollowed out, Bass all flubbed out but to be honest most one knob tone stacks are like that. I keep wondering if a 500pf might be more usable than the present 250pf?
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I think a lot of guys end up tweaking the values to get the sound they want.
So far, I've found the simple Big Muff "shift" control to be good with me. But I tend to use the tone knobs on the guitar a lot more to start with, and my ears aren't edumicated enough to pick up subtle differences anyway.
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Well, do you have a clear large photo of the inside of the amp now that it's complete? We might spot something that could be leading to hum.
Be sure to try tube swapping, if possible. Some tubes are just more prone to hum. Likely culprit will be your phase inverter tube; if this tube is prone to heater-to-cathode leakage, the large unbypassed impedance from the cathode of the phase inverter will lead to hum. The solution, since you can't bypass these resistors in the inverter is to select a tube with naturally lower leakage and hum.
Of course, there may be something else that we could spot in the picture.
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Both extreams settings of the tone stack are unusable---treble way hollowed out, Bass all flubbed out but to be honest most one knob tone stacks are like that. I keep wondering if a 500pf might be more usable than the present 250pf?
Well, you don't want to do that without modeling it some way, or calculating (I'd hate to go through calculations for this circuit). That's because the value of the resistors interacts with the specific values of both caps to define the mid notch. Willy-nilly changing values to alter highs will also change how wide the mid notch is, how deep and what frequency it is centered on.
There are other ways to turn that circuit into a tone control of sorts, but it would require more parts and not give you direct control over the bass or treble alone.
Another thought is that few tone circuits are have extremes that are "usable". Or they might be useful for a novelty sound. As long as something in the middle of the control's range is useful, that's probably good enough. I don't think anyone expects a single-control tone circuit to sculpt the sound like a razor.
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So I did what I suggested and modeled the circuit.
Original values have a mid notch centered around 800Hz. If you raise the 250pF cap to 500pF, the center of the notch drops to ~600Hz; increase that cap further to 0.001uF (or 1nF), and the notch will again move down further to ~400Hz. That will put the mid notch closer to Fender-like values.
The extreme settings of the tone control may still seem less than useful, because they'll try to strip bass or throw away all treble.
There might be some tricks to try with resistors to slightly isolate the tone pot to reduce the tendancy towards the extreme settings, but then it's not a Carmen Ghia anymore, right? What I mean is it might be a good thing to try if it's your amp, but maybe you don't want to muck with a customer's request.
I sim'd a few scenarios to tame the extremes, but I'd need to actually hear what it sounds like to know how to tinker it best. Tweaky stuff like this isn't solved by plotting curves but by trying and listening.
(In case your customer wants suggestions for wrangling the tone control, I see interesting stuff when the 250pF is rpelaced with a 0.001uF cap, a 15k resistor is inserted between the pot and its connection to ground, and a 10k resistor is added from the wiper to the 0.01uF cap. But this shifts the midrange notch down an octave, and may not fiddle the extreme settings the way they might want.)
Final thought: It seems to me Dr Z arranged this tone control to sound most-right near the middle of the tone control sweep. After all, this simulates the tone pot out of the circuit. I think the envisioned use of the tone control was slight changes to either side of center, rather than ever really using the extremes.
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I've been jamming on this amp with all my guitars-tele, strat, LP and more and more think the tone stack is fine. Just subtile movements make a big change. So if you are close to your sound and you want a little more treble---a 1/16" movement CCW might do it or for more bass--the same thing CW. I did some google searches about the CG tone stack and from what I read, it is normal to operate the way mine is doing. So I will leave it alone--it's just the CG personality. Main thing is, am I able to find a usable tone setting for all my guitars? answer--yes!
As far as the light hum. It does it with all the tubes removed--no DCV at all. The only way I could imagine the hum getting in the speaker is somehow the live heater wire too close to the OT plate leads that go to the power tubes. They are kind of close (1/8" in one place at 90 degrees in crossing) but when I moved them around with a chop stick there was no change. Can the OT generate any output without any DC power to it?? Other than that--some kind of current in the chassis somehow effecting the speaker through the speaker jack?? I've tried a bunch of things but nothing effects or changes the sound at all. This hum is not an irritating noise but all my other amps go dead silent when the standby is on, so I know it's not normal.
I am going to take a full set of pictures and post them but I've been kind of waiting for my 82K 3 watt resistor to come in and when I open it up again--take the pictures. I'm not really proud of some of my soldering and lead dress on this one. It was so close together, it was hard to make it look nice.
I'm really suprised that it is working as good as it is. It operates pretty quiet with single coils and really quiet with my humbucker guitars.
I was just wondering?? Am i the first one on this forum to build this ciruit?? Platefire
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Got the parts in today, thanks Doug!
On attached Phoenix shematic it showns cap C10 (optional .001) in parallel with plate resistor R20 on V1b. Also on attached Dr. Z layout the optional C10 is not there. So if the he copied this from his Dr. Z amp, I am thinking on some amps they included it and some they didn't or how did he determine it was optional?
I recall previous amp discussions paralleling a cap with a plate resistor to stop oscillation--but not sure? I got the cap, so I guess I could clip it in to see what it does.
I was preparing to do the finishing touches on this amp and was just wondering about it. Any help appreciated. Thanks, Platefire
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That cap would reduce the treble response of that gain stage. The person drawing the schematic might have felt the amp was brighter than he'd like, and drew in an optional way to tone it down.
I think most folks would agree that Dr Z amps are a little brighter or "more present" than some other amps, but I bet performers would agree it helps them cut through on stage it a good way.
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I talked to my Son on the phone today because he once had a Dr. Z Carmen Ghia several years back and ask him his take on it. He said that he got rid of his because of that brighter/more present tone that he said he couldn't seem to tone down. He said the gain structure worked great as far as break up. I recall him bringing it by the house when he first got it and had it running through a 2-12 cab but can't remember what it sounded like--to long. He did say it was normal for the tone stack to work like my conversion is working. Well I got some soldering and picture taken to do :icon_biggrin:
Platefire
BTW-Thanks HBP for the info on the cap on the plate resistor---now I know! I did clip the .001 cap in parellel with the plate resistor for V1b for a test and I couldn't hear any difference in tone regarding less treble. If any, too subtile for me to tell. I also clipped in the 25/50 cap on the 27V supply to PI and I couldn't detect any difference in gain or tone. So I'm leaving those two components out.
EDIT: Tagged some gut shots on this and next post. This is rough 40's/50's style P to P wiring. Not Pretty but it works!
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A continuation of gut shots started from last post. I will be posting some completed exterior shots maybe tomorrow. :icon_biggrin:
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OK, Here are the finished exterior pixs.
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Plate:
You have your red screen supply node wire running parallel to a (yellow?) OT primary wire. It's where that OT wire has to loop out and back before running to the EL84 socket closest to the sidewall of the chassis.
My guess is ripple at that screen node is being coupled into the OT primary wire running paralle to it. Try moving the OT wire with a chopstick (or other insulated tool) and see if that reduces the hum. If it does, you might have to cut that wire shorter to create a straight run perpendicular to the screen wire.
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HBP
I've tried to explain but somehow you have not read or understood my explination of this problem and that is this: ! The hum occurs with all tubes pulled and no DCV in amp whatsoever. Adding the tubes in and putting it under a load has no effect on the hum--it doesn't get louder or quieter.
So in my opinion the hum is somehow ACV--either heater or other AC somehow getting in to the speaker outlet and effecting the speaker. I don't know if the OT can have any output without any DCV into it?? just in case I moved heater wires around in close relation to the plate and cathode wires with no change. Only other thing I can figure is some kind of AC being transfered through the chassis? It's got me bumfuzzeled :dontknow: and I can't come up with an explination. Platefire
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Do you mean with the rectifier pulled as well? I guess the EL84 heater wires have a point at the terminal strip where they run parallel to an OT primary wire, which is on the other side of the terminal strip.
Or, maybe the power cord is too close to the OT. Or too close to the OT secondary wires.
Try dressing those secondary wires towards the corner of the chassis, away from where the power cord enters. If that helps a little, but doesn't resolve the hum, you may have to relocate the point the cord enters the chassis... probably where the "Remote Cabinet" octal plug is now.
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HBP
Yep with rectifier pulled also. Those secondary wires on the PT really have no where else to go. I have tried moving them around to see if it effected the sound, but no effect. To be honest the slight hum is so minimul, it's almost not worth worrying about. Once the amp is turned on, the amp noise actually drowns it out. Not that this amp ideling noise is loud but the noise don't get louder as you turn the amp up--so it is not noticable once you flip the standby to play.
You might have something about the power cord location because usually the OT is on the other side of the amp from the power cord but on the other hand--the OT should be non-operational without any power running through it---unless the ac normally transmitted from OT to speaker is being picked up somehow from the power cord and generating enough to make a hum. It seems though that moving those wires around like I've already done would change the intensity of the hum to some degree---but the intensity, however slight remains the same level whatever I do. Would the interrferance/hum be transmitted in the air or through the chassis? Could it be shielded? Platefire
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Well, it's like how an OT can pick up hum radiated from a power transformer. The large a.c. on the power cord can radiate a field around it's wires, which can be picked up by the OT and transferred to the speaker.
That seems like the only mechanism for hum when the rectifier is pulled. If it's minimal, and everybody's fine with the level of hum, then okay. If not (or for future reference), you want to keep the entry for wall power as far from the OT and speaker jack as possible.
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I used the same hole Baldwin used for their power cord, seemed they would have known better--so because of that, I used it too but I see what your saying. I think I'll let this one go as is and try to do better in the future.
I expermented with speakers tonight. Since my OT calculates with it's TR to be 5.26 Ohms, I hooked it up to my Silvertone 1482 Alinco 12" Fisher 4 Ohm that actually reads 4.1 Ohms, also my 10" Patriot Emenance Ragin Cajun cab rated 8 Ohms that reads 7.5 Ohms and a 10" Weber feromax rated 8 ohms in my DIY Champ and reads 6.5 Ohms.
The Weber 6.5 Ohms sounds the best. The notes were more compressed or touch sensitive. The tone was less harsh and more rounded. For some reason the noise factor raised a little bit on this speaker and there was a little overall volume loss in overall loudness in comparason to previous volume knob travel. Even with those two issues this speaker was more fun and enjoyable to play to the point it made me feel better about the amps performance. Platefire
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Gave this amp thorough workout last night going through all my songs lineup with the wife on piano and my JamMan backing tracks going through the PA.
The amp worked great. With the volume at about 9:00 Oclock and tone at 3:30 Oclock, my favorite tone was nailed with my Hwy 1 Tele. I had a little amp noise but when I switched my looper box to cut the two pedalboard loops out and go staight to the amp the noise disappeared--so the noise was in my pedals/pedalboard. Practiced a good 3 hours last night with no issues. The amp does seem to get pretty warm. Don't know if that's because of the compactness of it or not. The amp's touch responsiveness was very good, took my pedals with no problem and tone/sound coming through my 1-10 Ragin Cajun(7.5 Ohms) cab was very pleasing to my ears. This amp has a certain thickness and chime somehow all at the same time. Also this amp has a clarity of notes that just stands out. Put me on the list of a Carmen Ghia fans now with consideration for possibly building one for myself--but if I do it will be a larger chassis, turret board with plenty of room for a good layout. Platefire
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Excellent!
Regarding the chassis heat: if something didn't seem obviously wrong with the amp, you're probably fine. If I play my Deluxe or Super copies for 3 hours, they get pretty warm, too! :laugh:
I was in a little Nashville shop one afternoon when Brad Paisley came in to try out some amps. A good part of how his sound is distorted but dynamic, thick yet cutting, is the Dr Z amps. I was there when he bought his first Dr Z. It wasn't long after that other, bigger Nashville shops suddenly became Dr Z dealers (this was in 2000, when Dr Z had few dealers, and you still commonly bought your Carmen Ghia through ads in the back of Guitar Player magazine).
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Thanks HotBluePlates, Sluckey, PRR, John for helping me on this. I couldn't have got this far successfully without you! But----please don't quit on me yet! As much as I would like to be done with this project and move on, I feel like I must persevere with these other noise issues previouly mentioned/discussed. Knowing Randy is going to be using this in his studio I just can't feel right about it until I've done all I can do to make it silent as possible.
I had before mentioned that with the slight humm with all tubes removed I couldn't find anything that would effect the hum. Well this morning I took the cover off, pulled the tubes and tried some more.
I found that by getting some tin foil and wrapping it around the AC cord where it enters the chassis I could reduce the hum in some locations as I rotated it. Also I found by placing a jumper wire on the EL84 plate and touching the other end to ground killed the hum--so it is I think the incoming AC is effecting the OT. So as previouly suggested, think I need to move the cord entry location to behind the PT.
On attached Pix #3 below on tone stack. The white wires from 250pf passing by parellel by DCV power resistors/filter caps to tone pot, white wire to volume from tone pot and white wire from volume to V1b---I think might need to be all sheilded?
On attached Pix#6 I think maybe moving that yellow cathode wire running under the resistor and parallel to the heater wires and screen DCV wire would benifit being run above the resistor.
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For pic 3, I'm thinking the power supply will be fairly clean d.c. at that point, so probably no shielding necessary.
For pic 6, the cathode wire is a fairly low-impedance point in the circuit and is less susceptible to hum than a high impedance point in the circuit. I'm still more concerned by the OT primary wires running in parallel to other stuff in the chassis, which gives the opportunity to couple hum into a high impedance part of the circuit. See the pic below.
But relocate that AC cord first, then see if you still have any hum issue. You may find it essentially gone.
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Just completed relocating the power cord as per attached pixs. Cut the unused wires on the PT off shorter and re-installed a wire nut cap on each one. Also rearranged the OT wires to be perpendicular to the heater and screen wires. It's hard to tell in pixs but I have 1/8" to 1/4" clearance between the wires.
The disappointment is I plugged the amp to the speaker without any tubes in it and turned it on---it's still has that hum as before. Moving the power cord had no effect. I have the PT grounded on the OT bolt---could that be it? I've got the filter caps, PT, can cap, power tubes all grounded on the OT bolt---but the way I read it that in accordance with the Phoenix schematic!
Got to be an answer for correcting that hum where it would be dead silent without any tubes or with the tubes in and on standby. Platefire :BangHead:
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hey Bob. maybe it's transformer orietation. all the laminates are horizontal. If you could lift the OT
and try turning the laminates vertical and also rotating and listen while doing so may tell
you something. If no change it's probably just the PT internal hum coming through.
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I could understand if it had an internal hum coming within the PT but this is transferred to the speaker and when you unplug the speaker it's gone. The AC operation is somehow reaching/effecting the output of the OT. The OT is about 1 3/4" from the PT on this amp. We would never build anything on a new build that close---it just goes against normal layout practice.
Previouly with the power cord in the old position I did a test with some tin foil folded up with serveral layers and wrapped it around the power cord at the location where it enters the inside of the chassis to attemt some kind of sheilding between it and OT. It did reduce the hum eveytime it got in one paticular position. That made me believe along with HotBluePlates suggestion that maybe relocating the power cord would help. So now we know!
If I was to discover that re-arranging/rotating the OT in another position would help it, it would be a major headache moding the chassis holes, bolt holes and lead wires to work. Because of space, that's all you could do is rotate it horizonally. Platefire
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On a more positive note, I did some jamming on the amp last night using my tele (noisiest guitar) with no effects straight into the amp. The cranked distortion on the amp is something to rave about. Very focused and not flabby. I kept thinking Marshall tone. At 3:00 Oclock on the amp volume and guitar full volume brings you to a level where you get some great sustain for burning lead work ala ZZ Top
and turning your guitar down gives you a level of crunch rhythem that good support for vocals. Turning the amp volume up from 3:00 to full gives you even more sustained/harmonic lead levels--litterally screaming. It's just a little harder for land or find a good rythem level at that amp volume when you turn your guitar volume down, the slightest movement makes a big difference--kinda hard to control.
Considering the guitar I was using, the amp noise level wasn't bad at all. The very slight PT noise is still there and is only noticable when you first turn you amp on. Once you turn your B+ on the slight PT hum mostly buried in normal amp sound and it don't get louder as you turn the amp up. So it would be nice to solve this slight PT hum but I think I am nearing completing about all that can be done for this amp considering it is a old style P to P conversion is a limited chassis space. The amp's performace is very good. So I'm still open to suggestions on the PT hum. If not I'll probably sow it up and ship is very soon. I did tell the customer before I even started I was putting an un-proven reverse engineered schematic in a old cramped organ chassis and what he got he got. He agreed. Platefire
BTW-With my humbucker guitars LP & 335 the amp is very quiet. That is why I used my un-sheilded tele as a worse case scenario for testing.
Edit: Shipped it to customer 31 May 12