Dr Z Carmen Ghia schems needed

[Colas LeGrippa]

anyone has got a Carmen Ghia schem ?

Colas

[FYL]

Reverse-engineered, supposed to be accurate to some CGs (Dr. Z has made numerous mods to his amps).

[Colas LeGrippa]

thanks a million, phyl, you're a bro.

[jjasilli]

50uF on a 5Y3!!!

[Colas LeGrippa]

limit, if it sparks, you put a GZ34 that can easily handle 60uF.

[FYL]

50uF on a 5Y3!!!

A Sovtek, not a real 5Y3GT.

[Willabe]

A Sovtek, not a real 5Y3GT.

Ahha. Really a different rec. tube, with different ratings.


         Brad      

[Platefire]

Is there any legal problems with building one of these things using this scematic? I've got a request to provide a quote to build one. Platefire

[tubeswell]

FWIW Mike Zaite is DR.Z at the amp garage and is very helpful about discussing amps. e.g.: http://ampgarage.com/forum/profile.php?mode=viewprofile&u=8217. I'm sure if you asked him politely for schematic information he would be very helpful

[HotBluePlates]

Is there any legal problems with building one of these things using this scematic? I've got a request to provide a quote to build one. Platefire

If you build it, put "Dr Z" on the amp, and sell it as though it were one of his amps, then there might be a problem. No amp company is going to bother with coming after a guy that builds 1 clone.

[Platefire]

Well I just wondered because I had a dickens of a time finding a schematic. Turned out it was right here under my nose. The schematic here is a reverse engineered schematic. I figured because of the popularity of the amp, they would be all over the place/net. Doing google searches I found a lot of other people looking for it also. So it appeared to me they are making concerted effort to prevent it from getting out!

Long as the tube amp police don't show up at my door and try to arrest me for impersonating a Z.
Mine will be Dr. CC for Copy/Clone or Carbon Copy.   Platefire

[HotBluePlates]

Well, I'm building a Standel knock-off. While my comments above still hold true, the schematic and other information I have come from a person who was able to inspect a 1954 original, and reverse engineer every detail. Since there's a modern-day company who owns the Standel name, his request to me was to not disseminate the info he provided, nor build clones or drop-in boards, as he wants to protect himself from the possibility of a lawsuit.

So in that case, the lack of info is very few were made, few people have been inside them to know what exactly is going on. That, and a gentlemen's agreement to keep "being helpful" from coming back to bite him.

[Willabe]

Long as the tube amp police don't show up at my door and try to arrest me for impersonating a Z.

1'st off did you ever see a picture of our amp building friend? The one I saw he was wearing 70's big plaid pants and a button shirt, with my dads shoes, to each his own.   

But if the tube amp police/FBI show up at your door Plate and they've done there home work, I think you'll they throw you back in the pond.        

BUT, OTOH, WE KNOW WHO YOU ARE AND WE KNOW WHERE YOU LIVE!



                   Brad            

[Colas LeGrippa]

schems are useful for servicing. when I build an amp, i don't need no schems, I want to get an original design and tone.

[Platefire]

So--"I don't need no stinking badges(schematics)" and "Ve have vays of making you Talk"

I've got an old organ amp/chassis with EL84's I was planning for 18 Watt Marshall---thinking of making that a Carman Ghia Clone.

[Platefire]

OK, for you Carman Ghia fans out there and those Conversion Experts---if I gutted this Balwin chassis except for transformers, tube sockets, terminal strips----do you think I could squeez a Carman Ghia circuit in it? I would be the first to admit it would be tight if not impossible! Platefire

[DummyLoad]

as for the CG fitment? maybe.

did you trace PS ckt before gutting? pics are difficult for me to trace.

what i think the PS layout is...

the obvious.
reds - B+ 5U4
red-yel B+ CT.
yellows - 5V for 5U4 - duh! right?
oranges - 6.3V w/ 2 x 47R for virtual tap.
blacks - 120VAC
blues - ancillary FW PS.
blu-wht - CT for ancillary PS
white - bias??? looks like feeding 1/2 wave.

i have a baldwin organ amp i gutted a while back - mine was 45W - (6 x 6BQ5); 30W for the main amp (4 x 6BQ5) and 15W (2 x 6BQ5) for the effects amp. i dug up the PT and measured it. the lead colors and secondary arrangement appear to be identical to your PT.

all measurements are no load; all are AC RMS volts.

primary:
black to black - 120V applied and measured

sec. #1:
blue to blue 40V
blue/white to either blu 20V blue/white  is CT for this secondary.

sec. #2:
red to red - 600V
red/yellow to either red - 300V red/yellow is CT for this secondary.
red/yellow to wht - 87V

sec. #3:
yellow to yellow - 5.6V

sec. #4:
brown to brown - 7.1V

what's throwing me is the insulated can cap - usually used with V doubler PS or stacked for V divider; can't make out what's up with it. whatever purpose it served, it's toast.

--DL

[Platefire]

I haven't gutted mine yet. In fact I was looking at it this afternoon and I believe I will fire it up with tubes and measure the voltages and see what I got. The CG voltages are pretty low at 305V loaded to OT. Also power tubes are cathode R/Ground biased, so I can cap off that PT bias tap--won't need it. This will give me a good idea if it's allready in the right voltage range or if I need to knock it down a bit. I doubt it will be lower. After I've evaluated it enough and determined it is doable, then I will gut it.

The CG is pretty simple except it has some extra resistor/cap networks in the power supply that will take a little extra space. I was hoping to do it old style point to point without building a board. I think a 5Y3 will plug right in the 5U4 socket wiring and work fine, if I rememeber right?! Platefire

BTW-What's the deal on the 3M NFB resistor on the CG schematic. That's the same as not having any NFB??

[HotBluePlates]

I haven't gutted mine yet. In fact I was looking at it this afternoon and I believe I will fire it up with tubes and measure the voltages and see what I got. The CG voltages are pretty low at 305V loaded to OT. Also power tubes are cathode R/Ground biased, so I can cap off that PT bias tap--won't need it. This will give me a good idea if it's allready in the right voltage range or if I need to knock it down a bit. I doubt it will be lower. After I've evaluated it enough and determined it is doable, then I will gut it.

Do you have a schematic for the Baldwin? OR at least a model number?

Why not compare the schematic of the existing amp to the proposed new circuit to see what you might have to change (and what you could leave alone)?

BTW-What's the deal on the 3M NFB resistor on the CG schematic. That's the same as not having any NFB??

I'm not too quick on the up-take, but what I see is an inverting amplifier (the phase inverter + output tubes + output transformer) with a 220k input resistor (R19) and a 3.3M feedback resistor (R18).

In an opamp, the gain of the amp can be set by setting the ratios of the input and feedback resistors (specific values are less important). 3.3M/220k = gain of 15 from PI input to speaker. An alternate value of 2.2M is listed, which reduces gain to speaker to 10, which would give the impression of more headroom. That is, it would take a bigger phase inverter input signal to drive the amp to the same output power, keeping the preamp from overloading the output stage as much.

The "right value" would be determined by your ears.

You're just used to seeing Fender-style circuits, where the feedback resistor works against a resistor connecting to ground, and which then has to have a smaller value due to the circuit its in; R19 can be bigger than what you're used to seeing (often 47 ohm up to 1.5k), so the feedback resistor can be bigger as well.

[HotBluePlates]

I should probably model it to be sure, but...

The tone circuit in this amp looks pretty interesting. C11, C16, C17, R24 and R25 form a bridged-T tone circuit. This has the effect of putting a big mid-scoop in the sound. Basically, C16 cuts out lows, C17 cuts out highs, and when you add the two together you have lows and highs but no mids where they overlap. The tone control might slide that mid dip more towards highs or lows, depending on its setting.

Either that, or it "tilts" the existing lows or highs to be more dominant, giving a one knob circuit the impression of controlling both lows and highs.

[Platefire]

The tag off of the Balwin organ was Model 71 P. About a year ago when I gutted the organ I looked for the schematic and couldn't find anything on it. I just completed a loaded voltage test on it with the 5U4 and 5Y3 as follows:

1-590VAC to Rectifier
2-5U4=342VDC to OT, EL84 Plates=331/340, Screens=322/324
3-5Y3=320VDC to OT, EL84 Plates=311/320, Screens=307/307

So it looks like with a 5Y3 I would be right in the ball park of CG 305 to OT--about 15 volts over at 320 with a 5Y3(RCA).

HBP--thanks for the explination on the feedback circuit. Like you say, I'm use to fenders and never seen anything like that! From what I see I think I might proceed with the CG/Baldwin and maybe start another tread on it. One last thing though I would like to do before I start anything, is do a test on the OT to determine what the Speaker Ohm output it is. I've got an AC Transformer and formula to determine that somewhere, if I can find it. Platefire

[HotBluePlates]

Baldwin 71P schematics are out there, but you'd probably have to buy one. Justradios.com has them.

[Platefire]

OK, here is the link to testing/Caculating unknown OT to determine impediance.

http://sarris.info/main/calculating-output-transformer-impedance

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 (16 Ohms??)

Have I done this right??? Platefire  

[DummyLoad]

Your math is correct. 12.2k into 8 ohms
 If you doubt that, measure again? Do you have a signal generator with some oomph? If yes dial it up to 1KHz and measure.  Baldwin may have been running fixed bias very conservatively. Looking at the photos, it seems that way. I can't trace a cathode resistor off of the output tubes. But then again, maybe it's that power resistor tied to the insulated can cap?

--DL

[Platefire]

DummyLoad

So is this good to run a 8 Ohm speaker?? I've already measuered serveral times, so I'm sure that's right! 

The bias circuit is located opposite end as the transformers. Two green wires from PT supplys 18VAC each to two diodes. The end result is a -20VDC to each EL84 input grid. The cathodes goes straight to chassis ground.

There is quiet a bit of wiring going to 3 sockets in the chassis that accepted plugs that went to other parts of the organ. Very busy scatter-brain point to point. Platefire 

[jojokeo]

Your math is correct. 12.2k into 8 ohms
--DL

Plate, I think you could fit it in there, especially going p to p. Simply draw an actual size chassis on paper and lay out the components as close to actual size as possible until you fit everything in there. Then build by copying your drawing. I love doing this. You get better everytime you do it.

Wouldn't it be more accurate to use 6.5 or 6.6 instead of 8 ohms due to an 8 ohm speaker's actual measured resistance? This would yield the more likely and common 10k:8r OT you'd commonly expect to find. Either way, it's no big deal and close enough.

I've seen this schem a bunch of times over the years and the PI always throws me off the way it appears and also tied to the power rail the way it is. Can someone tell me what kind it is & break it down for me or maybe re-write it to make a bit more sense when looking at it???

[VMS]

You guys probably already know this, but according to this thread the original CG was a modified Hammond AO-35 and it was built into the same chassis:

http://www.tdpri.com/forum/amp-central-station/143261-speaking-hammond-ao-35-carmen-ghia.html#post1953445

[Platefire]

Yeah, I think it could be squeezed in there. I just dread all the de-soldering and re-working to prep it for the CG. As far as the OT, I'm still a little fuzzy with the results of the equation? 12.2K what does that mean? is that 12.2 Ohms or is that something else? Impediance and Ohms

Also Very interesting on the Hammond AO-35 regarding the link on the previous post. On the thread I read the arguments on both sides that the CG is or is not related to that amp but---looking at the schematic I would say it's to close to be a coincidence!

I've got a customer wanting me to give him a price on the CG, so I guess I'll give him a price for converting the Baldwin 71P and a new one and let him choose.

BTW--Here is a Hammond AO-35 to compare to CG.  

[Platefire]

The customer selected the option to convert the Baldwin instead of a new amp. So I guess from here I'll start a new thread. 

BTW-I told him I had no way a verifying if this schematic is actually a Dr. Z Carmen Ghia since I don't have anything to compare it with other than the rumor that is was originally contrived from a Hammond AO-35---and it was modified from that---so using that so called reverse engineered schematic---he gets what he gets!

Platefire