Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on August 16, 2016, 12:58:51 pm
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Guys I am progressing on the conversion of my Baldwin Orgasonic organ amp that I made some years ago. I have the chassis basically gutted and am looking at tube placement. There is one octal socket near the edge and a hole there next to it that could be enlarged with around 5/8 between the edges of octal tube sockets if I did that. The 6L6-G that were in the amp were in octal sockets mounted nearer the center of the chassis. I would like to use those for the bassman 6L6GCs, and for space issues if I use KT66 in the future, but if I do the power tube sockets will be underneath the turret board, but sort of to one side of it. I've been thinking about it and two things come to mind. Testing and repair if necessary in the future. Since I am using a Hoffman board I see that I could check the screen, grid and cathode voltages on the board end. I would have to install a test terminal to check the plates and filaments. I suppose I could install a test terminal strip out in the open somewhere with the power tube pins connected to dead end terminals. Another thought was to check from the outside/topside of the chassis somehow. For repair the pots and inputs could be undone from the chassis and the board unbolted and swung up out of the way. The chassis is 2 7/8 deep so mounting the turret board well above the power tube sockets is easy to do, and in fact I have planned on elevating it some, say and inch or so.
I wanted to see what you guys think of this before proceeding to drill anything. A pic is below.
Another question I have is the choke. I intend to use this big original choke. The schematic says 8 W or 8 H I cannot tell for sure, and 30 ohms which I can make out clearly. I am sure it is probably overkill for a 5F6A but don't know for sure. I do have a 22699 bassman choke that I could use, which would lighten the weight of the chassis considerably. If I don't use the original choke HPB has in the past already spoken for it.
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I would use the bassman choke.
I would not put any sockets under the board. That's tempting some possible regret. I would punch two new socket holes and move the OT. Maybe even put a cover plate over those socket holes...
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Thanks Sluckey - I suppose I could cut the two new holes easy enough with the drill press. Why would you move the OT?
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To get it away from the sensitive preamp end of the board, input jacks, volume tone controls, etc., and down close to the output sockets. The Hoffman 5F6A board was designed to work with this layout.
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OK, I'm going to use the 22699 Bassman choke, and I am going to cut an 8 x 4 inch piece of stainless sheet metal like the piece already on the chassis to cover the area where the OT was and the two octal holes in the middle as well as extraneous other little holes in that area. Then I will drill another octal hole on the edge near the one octal hole. The Baldwin choke weighs 5 lbs 15 oz. and the 22699 choke weighs 15 oz - so that is a weight savings of 5 lbs! The cabinet will appreciate that.. I can then relocate the OT to the new piece of stainless and all I have to do is drill 4 mounting holes and two wire feed-thru holes.
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In my picture (above) that black thing on the bottom left is the Baldwin choke. This pic (below) is what it looks like now, and you can see I have more room, with that big choke gone, to drill another octal hole to the left of the one that is along the bottom edge.. I can mount the 22699 Bassman choke in the center line, leaving room for the new octal hole. HPB this Baldwin choke is yours if you still want it, just pay shipping in a flat rate box.
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I might cut a new piece of the stainless sheet metal that is longer, like 10 inches in length, 10 x 4 , and take that piece that is on there off, and replace with one piece. It would look better.
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In my picture (above) that black thing on the bottom left is the Baldwin choke. ... HPB this Baldwin choke is yours if you still want it, just pay shipping in a flat rate box.
Oh, jeez! Now I'm gonna have to build a choke input class A amp around that choke! Sure, if you have no other plans for it, I'll take it. I'll PM with details.
Thanks!
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Want another one? Nobody should have to go through life with mismatched chokes.
Organ chassis can be problematical. I think we've had this discussion before.
I strongly suggest you place your tubes where they will go; get a piece of cardboard the size of the parts board you are going to use, and just be sure you have the room for the controls. As I believe we've had this discussion before, I'll stop.
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I share your concern eleventeen - I think I'll have enough room in this chassis for the hoffman board and the controls, tube wiring, etc. I wanted to re-purpose some Sprague Atom 20uf 600v caps for the first filter node but they are too large to fit nicely in the PS end of this chassis, and still have room to fit the other caps. Still looking at a vertical mount for the other caps... maybe I can squeeze them in there..... It's got almost 3 inches vertical but as you can see not a lot of horizontal area...
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I'm also thinking I might not have a sufficient OT. This Baldwin OT was for two 6L6-G tubes and it has 8 and 16 ohm taps. I might use this one that has 2,4,8 ohm taps.. http://www.classictone.net/40-18000.html (http://www.classictone.net/40-18000.html)
and a decent price.
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I'd think your existing OT would be perfectly fine if you are making a dual-6L6 amp. I forgot whether you started with a 2x 6L6 Baldwin chassis or a 4x. Admittedly you may be lacking the 2 ohm tap on the secondary, but I would just re-wire the speakers to a 4 or 8 ohm configuration. Will that affect tone? I can't tell you. I know we want to do all mechanical work (eg drilling holes & mounting components) before lashing up the wiring but the fact of the matter is that even though it is physically big, changing out a standup OT (after the rest of the amp is assembled) with appx the same footprint is not the biggest of big deals....if you have a drill press or can otherwise control drill depth. Yes, the steel chassis does not make things easy.
You may be forced to consider some type of doghouse for your cap collection. Sometimes I make a board type deal and silicone a row of PC-mount caps to it. That would be under the chassis, if you can find room. On top of the chassis, perhaps under a plexiglas insulating / protective square mounted on standoffs. At least those PC mount e-caps are cheap.
As you can see and which I hate to rub your nose in, the tight dimensions of that particular chassis create certain problems that can't be easily escaped and which force you to do non-trivial work to get around. I feel your pain on this one, I have that exact same chassis and I have stared at it for a long time without starting anything on it because I run into issues I am not eager to deal with.
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I agree. That OT is fine.
That big choke was there for a reason. Baldwin probably didn't use a 5lb choke if a 1lb choke would work just as well. The size of that choke indicates that the entire B+ current flowed through it. And that means there's a chance that the power supply used a choke input filter. Did you draw the schematic of the power supply before you gutted the chassis? And here's a question for you that may make you change your mind about giving away that huge choke. How much AC voltage do you measure between the HT secondary and HT center tap?
Most times it's advisable to keep PT, choke, and OT together because they are proven to work well together. If the original amp had a choke input filter then you will need to use the same choke input filter. Otherwise, your B+ will be very much higher than you will probably want.
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Here's the schematic for it. The choke is on the ground side, so I don't think this is a choke input PS .
(http://i122.photobucket.com/albums/o250/privateacct/Baldwin%20Orgasonic%20Organ/20120409_0639.jpg)
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Sluckey - I'm getting 442VAC from one lead to center tap on this PT unloaded ..
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That's the classic choke input filter. Choke can either be on the positive side of the rectifier or the negative side. Makes no difference. Without that choke your unloaded B+ will be 625VDC! Better hang on to it.
The attached is from RDH4...
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Well guess I better tell someone that I am keeping this choke ..
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OK so what would you do if you are going to make a 5F6A bassman circuit with this iron setup. Would you use the choke on the PT secondary center tap to ground as in the Baldwin, and omit the Bassman choke, or would you use this Baldwin choke as it is used in the 5F6A circuit? I'm thinking that if I use this choke on the center tap to ground, then another choke would not be necessary in the PS.
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Excellent point brought up by Sluckey and you owe him a beer. That PT is a monster that puts out essentially 900 volts CT no load. (I remind you, I have that same chassis and those trannies and I have measured it/them; both volts and inches. That chassis sits on my junkpile with the OT removed) The choke being in the CT doesn't much matter, ALL B+ current flows through it and with or without it, your B+ is gonna be really high, figure 440 * 1.4 = 616 volts minus 50 or so for a 5U4 and minus 10-15 volts for choke input = 550 volts, 520 under load. Very high, almost 100 volts high.
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OK so what would you do if you are going to make a 5F6A bassman circuit with this iron setup.
The only reason I'd ever use that PT to build any guitar amp would be just to see if I could. The last project I did was a Hammond AO-63 conversion. It used a (swinging) choke input filter so I had to do the same, otherwise, my B+ would have been sky-high.
But I'm a tinkerer and I understand wanting to use what you have and convert it to something you can use. I'd put the choke between the cathodes of the rectifier and the first filter cap. (Look at the power section of this schematic) (http://sluckeyamps.com/hammond_2/AO-63.pdf) And the center tap straight to ground. And tape off the center tap on the 5 volt winding.
You need to use this choke with this PT.
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> classic choke input filter
IMHO-- this is neither fish nor fowl.
Cap (26) is clearly in the "Cap Input" position. No-load it will charge to Peak of AC, 618V.
BUT a "good" cap-input cap for a 200mA amp would be 200uFd. Here we have just 4uFd, 1/50th of "good". We suspect it may sag.
Duncan PSD shows C(26) voltage going to 575V and to 300V on every half-wave. WAY too much ripple! Then Choke and C(2) filter that to about 435V (averaging the 575V-300V swings) with 20V p-p ripple, an acceptable value.
As you say, true cap-in tends to 618V, true choke-in tends to 398V, and this is something else.
_I_ think Baldwin were not as dumb as they look. The 4uFd 8H 4uFd makes a very reasonable B+ with a minimum of capacitance.
Why minimize caps? E-caps are cheap? I bet this is OIL Caps. E-caps fail. When you sell to churches which have stood for a hundred years, they don't want to find dead caps every 5 10 20 years. Oil caps will last longer than the rubber on the line-cord. This is a lifetime power supply. Assuming you KEPT that oil-cap bank, didn't chuck it out.
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Sluckey thanks for the assistance and the info you have provided. I have certainly learned something. So it looks like I am at a fork in the road. I could use this Monster PT with high voltage and current capability along with its Monster Choke and try to finagle a 5F6A sort of circuit.
Or, I could source another more appropriate pt, in stand up configuration that I could use by covering the existing pt hole in the chassis with a bit of my stainless sheet metal. Going this route may cost some, but I would also gain better more suitable voltages for the 5F6A, more area in the chassis where I could use my 600V caps, and not use that boat anchor choke.
I already have a cabinet made but not covered for this chassis.
Would this be a suitable PT for a 5F6A in your opinion? http://www.ebay.com/itm/PT330M-USA-POWER-TRANSFORMER-TUBE-AUDIO-330-0-55-330-x140mA-/15214569578 (http://www.ebay.com/itm/PT330M-USA-POWER-TRANSFORMER-TUBE-AUDIO-330-0-55-330-x140mA-/15214569578)
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Thanks PRR yes I still have the big 4uf oil caps.. which appear to be sound. The problem with the 4 uf oil caps in doing this , is they were mounted down on the opposite end of the chassis, which would now be the preamp end of a turret board.
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OK so what would you do if you are going to make a 5F6A bassman circuit with this iron setup.
... I'd put the choke between the cathodes of the rectifier and the first filter cap. ...
I wonder about how much insulation rating the choke has since it was positioned from center-tap to ground. Sometimes that is a reason for not using the choke between rectifier cathode & cap (lower voltage from coil to case). Or maybe the arrangement is just a clever way to get something between cap-input and choke-input voltage from the power supply, as PRR points out.
OK so what would you do if you are going to make a 5F6A bassman circuit with this iron setup. Would you use the choke on the PT secondary center tap to ground as in the Baldwin, and omit the Bassman choke, or would you use this Baldwin choke as it is used in the 5F6A circuit? ...
OR use the Baldwin plan of choke from CT to ground and add the normal Bassman choke between plate and screen nodes. I doubt this route will be well-received, but I did just build a 1/3w amp with two chokes on board (though they are both physically small).
But my overall inclination would be (as I've often said, maybe even about this project before) to keep the entire PT, power supply, OT and output tube setup as it was in the original circuit, then change the preamp/phase inverter to the desired amp circuit.
... The problem with the 4 uf oil caps in doing this , is they were mounted down on the opposite end of the chassis, which would now be the preamp end of a turret board.
That's probably a non-issue, except for any consideration of space.
Have you already bought the 5F6-A board? If not, and you keep the power supply & output stage, then you don't need the room for the bias circuit and can mount screen resistors and grid resistors on the sockets. You could likely get a custom board which just has the preamp and phase inverter...
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Hi HPB - no, I make my own boards, and I haven't drilled any G10 yet (thank goodness) . Interesting idea about the custom board.
Wow, I see Doug has a Heyboer PT for $70 with super specs.. Nice.. Mojo 762...
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I think if I am to proceed with this PT and Choke, I would use Sluckeys AO-63 power supply as a guide.. He used a GZ34 so a 5U4 would drop the voltage some... maybe like 435v instead of 475v.
Then I would have to use a tap off the secondary for the bias voltage..
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I wouldn't bank on such a large drop... Maybe more like 450vdc (or a bit more).
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I'm going to sleep on this whole project, part of me says like eleventeen to put it on the junkpile, and another part says give it a go.. but I have a Super Reverb project in the wings and as much as I would like to hear own and feel a 5F6A bassman it may have to wait. Many thanks to all who have provided input and ideas... :icon_biggrin:
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One more thing to consider... This chassis was a power amp only. The layout is fine for a power amp that deals with power amp level signals. Trying to shoehorn a guitar preamp into a power amp ONLY chassis can sometimes be very challenging. You need a spot on the chassis that is out of the way from all the big signal, high current stuff, reservoir caps, OTs, etc. And you usually need a well thought out layout that may not look much like a production guitar amp layout. It's usually easier to just restore the power amp and build the preamp on a separate chassis, maybe even bolted to the end of the power amp chassis. You can still power the preamp from the power amp supply.
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> Maybe more like 450vdc (or a bit more).
Duncan PSD says 482V, with 5U4 and default winding resistances. (2K DC load, which approximates full output in a 4KCT OT such as 5F6a.)
Rising to 533V with 5K load (roughly 500V at the ~~100mA a Bassman usually idles at).
In retrospect, this was probably a fine Power Amp (most older organs are), and would have been a fine guitar amp (maybe without the rude growl of some g-amps). Of course it's been torn up to try to fit a preamp where none was intended.
Hmmmm ... seeing it was 6.6K load, and cathode bias, I wonder if the current rating truly matches a 4K load fix-bias. (It would be alright because it was over-built for long-term church use, and a fix-bias amp idles some time and then runs much lower current.)
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I think the "separate preamp" notion was where we arrived the last time one of these particular Baldwin projects was being tossed around.
This PT is not going to produce a 5F6-sounding 5F6, IMHO. I think it will be a lot cleaner with 80 more volts of B+ unless you use zener voltage reduction = yet another physical assembly you have to create in an already cramped space because you will need high wattage zeners on heatsinks, several of them.
To make what I said earlier clear: This thing is not on my junkpile because it's junk, it is there because after buying it and shipping it here and staring at it at reasonable length, the sum total of the rigamarole I could see that would be required to 1: reduce the B+ to the output stage and 2: super-reduce the B+ to the preamp stages, 3: cram the parts in in a way that let's face it, there is always a risk that the thing will turn into an incurable hum monster with an improvised layout, 4: end up with a kind of awkward 3" tall chassis 5: have to work thick steel (vs alum) added up to an amount of time+money+effort with which I could buy a Mojo chassis....that would fit everything in on a known basis....and be able to accept a faceplate to make the final product look nice....and be done with it. Yes, there was an easy $70-$100 extra work getting it in shape as I saw it then and see it now.
I don't mean to discourage. I hope you understand that.
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Hey eleventeen - I understood what you meant, no problem bro, I have a pile too..and not all of it is amplifier stuff. :-). This thing has sat in the "junk pile" room for nearly 2 years now being totally neglected. Ah well I have many original Fenders that don't get the attention they deserve either. But I do drag them out and turn then on from time to time, maybe the intervals are too long though. Anyway, it was just time for me to make a decision on this one and get it done. I am trying to reduce the pile some.
I had already installed a rack of diodes on the center tap to lower the B+, the terminals fit nicely beside the PT end bell on the side of the chassis. The steel doesn't present that much more of a problem for me. Have drill press, grinder and carborundum discs will travel, LOL. What I could really use is a metal brake and some hole punches. I actually have a faceplate fashioned but it's not drilled, stained and finished yet. It's thin hardwood and with a wood burning tool the controls and such can be labeled, ala Ken Fischer. I wasn't considering building it to sell it, so as long as I like how it looks it's good enough.
So, this PT is not suitable for what I want to do with it. Having a PT with a bias tap would be nice too. Now if I used a stand-up Bassman PT on this chassis, the goal of making a Hoffman 5F6A could be achieved. suitable PTs are not cheap, but it seems the only viable solution for this project. So I'll look for one for as little coin as possible.
Who in the world would want this Baldwin PT? What use would it be to someone? Or is it really a boat anchor destined for the scrap heap? I really wouldn't want my relatives burdened with it after I pass on.
Sluckey, PRR, eleventeen, HPB - many thanks for all your input, it is much appreciated and respected.
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Have you folks seen this about back biasing? Looks like I could drop some PT secondary voltage this way and also get my fixed bias voltage.
http://www.aikenamps.com/index.php/what-is-back-biasing (http://www.aikenamps.com/index.php/what-is-back-biasing)
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Very interesting set of circuits there.
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Ok guys, lend me your judgement here.. which one of these would be best for a 5F6A build? (these are two reasonably priced stand-up PTs)
http://www.edcorusa.com/xpwr178 (http://www.edcorusa.com/xpwr178)
or
http://www.edcorusa.com/xpwr172 (http://www.edcorusa.com/xpwr172)
And am I safe to assume that all that would be required for using one leg of the PT HV secondary (330v leg) is to adjust the value of the bias range resistor on the Hoffman 5F6A turret board?
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Either one of those, prefer the 330-0-330 volt one as it is closer to 5F6 specs....Believe it or not, earlier 5F6 used an 83 rectifier which is a mercury vapor tube....with VERY low voltage drop. Play too loud, not only the cops but the EPA shows up!
I think I would go with the higher voltage one, but let's wait til some more tweed-oriented (than I am) guys chime in.
You could certainly use a 150 ma model if they make one. 200 ma is getting on to Twin (4x 6L6) range.
"And am I safe to assume that all that would be required for using one leg of the PT HV secondary (330v leg) is to adjust the value of the bias range resistor on the Hoffman 5F6A turret board?
Absolutely.
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I like the 172 better.
And am I safe to assume that all that would be required for using one leg of the PT HV secondary (330v leg) is to adjust the value of the bias range resistor on the Hoffman 5F6A turret board?
Yes. New value will be approx. 100K.
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I think you already know my vote: Use this chassis almost exactly like it was to start with.
Everything works well together in the original plan, and you can adjust the 3.9kΩ feedback resistor if it's too polite. The paraphase inverter probably adds some welcome color to the sound, and you already have a built-in master volume.
I've built an amp with a split preamp/poweramp chassis, and it's still running along beautifully. It would surely be less money to build only the preamp chassis and use a cable between the two...
Despite the other recent thread showing Gibson using a cathode follower output from the preamp, you probably don't need it for any reasonably-short cable run (I sure didn't use one).
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Sluckey -that was what I was thinking concerning the bias range resistor. I was going to figure it out using 10-15ma current as a guide. Thanks.
HPB - I have to say sorry, there is no going back to the old circuit. I look at tweed bassman amps and wonder why everyone is worried about hum. Some of those tweedies were pretty tight chassis and they didn't exhibit a lot of hum. So I am determined to make a Bassman 5F6A in this chassis. If it doesn't work, I can always yank the turret board, tubes and sockets and OT and use whats left for target practice.
I do hope the big choke winding insulation can take the higher voltage, you did bring up a valid point. So I guess I'll see.
Plus - I have a set of EL34s that might be good in this amp. Up the screen resistors to 1.5K 3 watt and make sure the screen voltage isn't over 425v and all should be good. So, I guess it won't be a stock 5F6A but
might be a nice amp anyway.
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Incidentally, this is pretty kewl...
This is a mercury vapor rectifier powered 1000 watt amplifier and the guy is feeding a low frequency signal thru it. He is apparently in Europe where the power line freq is 50 Hz. Check out the behavior of the rectifier tubes when he drops the input freq 1 Hz at a time and gets to 25 Hz. Near the 4:00 minute mark.
https://www.youtube.com/watch?v=M_rdZsZasVk (https://www.youtube.com/watch?v=M_rdZsZasVk)
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I just noticed that I could also use dual 5U4G rectifiers instead of a GZ34.
I don't think so. Isn't the attached pic the same as your chassis before you gutted it?
One 5U4 is capable of providing all the current that a pair of 6L6s will want. Now the Baldwin 45 looks almost like your Baldwin 40 amp except it has 2x5U4s, 4x6L6s, and bigger PY and OT. Are you maybe thinking of the larger amp?
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Imagine if his amp was the 4x 6L6 and dual 5U4 version....if only the PT had dual 5v windings he could place 2 qty 5U4 in series (second one half wave, plates connected in parallel) for his voltage drop! Good room heater, too.
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I could say you are "quick draw Sluckey" LOL .. I didn't get that one deleted quick enough. The reason I deleted it was I remembered that voltage drop might be the same, output current level doubled, but the filament current would also be twice that of one tube, and since my PT only had one I don't know if it would handle it.
The reason I was asking is that upon looking at the 5E6a I see it has twin 5u4s and it is the predecessor to the 5F6a. I read that Leo switched to a GZ34 in the 5F6a for better current handling. So I thought, maybe I could use dual recto, but no.
Also it occured to me I could simply install an additional capacitor filter node before the B+ node to knock some voltage down and reduce hum and noise. A bleeder resistor would also drop a little.
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There are many options to drop B+, including the way it was originally done using the big choke. :icon_biggrin:
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It is possible that this PT and 6.6K OT would be better suited for a 5E5A PRO build. Or maybe a 5F4 Tweed Super.
IMO... The only way this PT is suitable for ANY Fender guitar amp is to use it with that big choke wired as a swinging choke, ie, choke input filter circuit.
You need to use this choke with this PT.
IMO... Without using the choke as it was intended that PT will put out 442VAC which equals 442 x 1.414 = 625VDC unloaded. It's simply ridiculous to try to reduce that amount of B+ for use in the Fender amps.
IMO... Use the PT and choke as a paired set or get an appropriate PT.
You need to use this choke with this PT.
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Arrrgh! I see you're posting and deleting again.
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Sorry .... was entertaining the idea of the other Fender circuits because of the Output Transformer being 6.6K input inpedance . I am going to use the big choke , I wasn't thinking of not using it . But I squashed the idea and deleted that post, again sorry..
Steve did you think I was talking about the PT?
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Steve did you think I was talking about the PT?
Of course. Based on your deleted question, how could I think otherwise?
I've run out of things to say about this PT, choke, and OT. Maybe someone with some fresh ideas can add more.
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This is what I deleted (paraphrased) "Maybe this amp is more suitable for a 5E5A or a 5F4 build based on the 6.6k OT?" I don' t know why you thought it was a question about the PT and choke. Again I apologize.
I appreciate your help and input. I have another little problem to deal with, which is making two holes for the power tubes so that one of them will clear that big choke. As previously planned it is very very close to it.
So I think I am off to Home Depot or Lowes to see what aluminum they have in stock. Cutting stainless with a grinder isn't bad, but drilling 1" holes in it isn't too much fun.
There won't be much posting on this thread for a while on my end..
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This is what I deleted (paraphrased) "Maybe this amp is more suitable for a 5E5A or a 5F4 build based on the 6.6k OT?" I don' t know why you thought it was a question about the PT and choke.
No it's not. This is EXACTLY what you said...
It is possible that this PT and 6.6K OT would be better suited for a 5E5A PRO build. Or maybe a 5F4 Tweed Super
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Well take me down to the shed and smack my pee pee. I am telling you for a fact that I was thinking of the 6,6K rating of the OT. Plain and simple. I AM and WAS not deviating from using the PT AND choke, as we had already talked about and determined that they need to be used together. Sorry I bothered you. But there is a DELETE button, and if it's not used for deleting something you decided very shortly after posting that you don't want to say, then tell me,. what is it for?
And you could have deleted your reply as well... then all would have been good...
I will excise the delete button from my usage, never to use it again... I will be a good boy and try not to post anything without thinking it totally through. OK?
Cool have a nice evening
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But there is a DELETE button, and if it's not used for deleting something you decided very shortly after posting that you don't want to say, then tell me,. what is it for?
The delete button is there for you to use as you see fit. I've used the delete button. Lot's of others have too. The downside to deleting a reply comes when someone has responded to your reply. Now that response is just dangling and usually doesn't make any sense to others reading the thread. And it can be frustrating to the person that made the seemingly stupid, disconnected response. You just deleted two posts that I had replied to, so my frustration was a bit more than normal. Today that's OK.
What was even more frustrating than the fact that you deleted the replies was that you came back and tried to tell me you said something different than what you deleted. But I had quoted your original reply word for word so there was no question about what you said.
No harm done. I'll just continue to use the quote button whenever replying to your messages.
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Nope sorry - I did not try to say anything different. If you think you can read my mind based on written words, be my guest. But, calling my integrity into question isn't really prudent. I have stated what I meant in the first deleted post, and again in my paraphrase of it. Your interpretation and subsequent post was off base and you don't seem to be able to understand that, and it is especially rude of you to not accept what I have told you.
So no harm done. I will continue to post as I always have.
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Additionally, Sluckey, if you have a beef with me, put it in a PM and not here in my build post.
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No beef. No pms. I'll just stay out of your threads.
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Well - after some time getting this thing re-configured, and a couple medical problems, I have gotten the board installed and wired up. And upon firing it up I have 425vac on the PT secondary leads to ground at the rectifier. I would say more but I am dead in the water until I get another bias capacitor and replace the diode and range resistor. I installed that bias diode backwards for the first time in my life. Smoke city. This board has not been easy as the layout is inverted from Hoffmans layout.
Sluckey, I think I am going to need more than 1K on the bias tap but when I get it working again I guess I will see what the voltage range is. I have not installed a rectifier yet, obviously, and I think I'll disconnect the bias tap until I get all the other voltages on the PS rail ironed out.
I do have a 52v zener I could install on the PT secondary CT if necessary, but I am anxious to see what kind of V that choke is going to drop, or if it will even work in this configuration and not short out.
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I am also waiting for a 470 ohm 3W resistor so pls disregard that sand cast one. Also I can just leave the bias range resistor out and leave the bias tap connected until I get the PS node V's sorted.
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OK with a 5U4GB installed I have 505 vdc on PS node A. This is unloaded, no other tubes installed, and the bias circuit disabled. It would appear that the choke, rectifier and first PS filter caps are dropping 350vdc in this unloaded state. I really don't know how much voltage the circuit is going to drop when all the tubes are installed and biased properly.
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IYes. New value will be approx. 100K.
I was thinking of a 220K to start off with ...
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Well since you have blocked PMs from me
Steve hi how are you? Look I don't understand why you are so worked over such a trivial thing. Can't we let this bad water go under the bridge?Can't we be friends? I harbor no animosity towards you. I could use a little help with this Baldwin. I tried a 52v 50w zener on the PT CT and instead of dropping the high voltage it raised it. At the time I had one 12AY7 plugged in to get some sort of current flow on the power rail. 515 vdc is just way too high to operate at. I will have to change the first two ps filter caps to series config and bleeder strapped. I was able to sub a cap into the bias circuit and inserted a 220K range resistor and got a sweep of -25 to -40 volts, which of course willdecrease it I ever get the high voltage decreased. I know it's not enough for the 6L6's. OK thanks..
the zener I used is an ECG5277AK
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And by the way Mr. Luckey you are punishing no one but yourself .
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... I tried a 52v 50w zener on the PT CT and instead of dropping the high voltage it raised it. ... the zener I used is an ECG5277AK
The ___AK part is the correct type, with the zener cathode bonded to the case. As long as that cathode is connected to chassis ground and the anode is connected to the center-tap, you should be getting voltage drop. You'd measure that with your meter's black lead on the chassis and the red lead on the center-tap, with a reading of -52v (or a bit less since you're not drawing full current).
You're already aware of the issue of your amp's bias voltage being dependent on the reduced B+ due to the zener.
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HPB - thanks the zener was bolted to the chassis near the pt. I did read a v drop of 50 volts across it. But for some reason now I have higher voltage on the pt secondary and the rectifier. It was 505 before zener and now its 515 with Zener. Strange.
I am going to change the plate filter node to two 100uf 450v caps in series with bleeders, I am worried about exceeding the 500v rating of the two 22 uf in parallel. Also HPB I can raise the bias range more negative by changing the bias rng resistor. I've got a 220K in it now. I was saying if I got the high voltage down the negative voltage on the bias tap will be reduced too so I would have to decrease the range resistor value to get it back up.
Really I kind of expected this to not work out. Proabably have to shove it into the closet and forget about it..
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HPB - thanks the zener was bolted to the chassis near the pt. I did read a v drop of 50 volts across it. But for some reason now I have higher voltage on the pt secondary and the rectifier. It was 505 before zener and now its 515 with Zener. Strange. ...
If the winding is 425vac, that implies 601vdc unloaded. If there was a load, you might have voltage sag due to the rectifier & PT winding resistance.
I suppose it's possible that with the reduced PT voltage (375vac after 50vac zener-drop), leading to a lower unloaded voltage of 530vdc, that the current draw could be lower, so a reduced apparent voltage drop. But it depends how much current & what was dropping it: going from ~100vdc drop to ~15vdc drop seems a little odd (though perhaps not impossible).
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HPB - this is so odd... I removed the zener, and reconnected the PT CT to ground. Now I have 525 vdc at PS node A the plate supply. I now have -40 to -60v dc on the bias circuit measured at the 220K resistors. The bias is good enough to install some tubes but I am hesitant to do it not knowing what to expect. It's like the zener wasn't even there. I wonder if a 50w zener needs a certain level of current to work properly?
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OK update - I installed a couple of old 6L6 and turned it on. I now have 447 vac at the Pt secondaries and 421 vdc on the plates. Much better. I now have -47 vdc on the bias swinging up to -70 vdc.
So I need to adjust the 220K bias range resistor upwards a little, to like 250K. What a difference a couple of power tubes and some current make.
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In a previous post I stated one of the bias caps smoked.. yes it did, but it was because I had a 1K bias range resistor in there by mistake and the high AC voltage exceeded that poor little 100v caps voltage rating and the plastic coating on the outside was literally burning up.. hence smoke.. my bad..
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OK update - I installed a couple of old 6L6 and turned it on. I now have 447 vac at the Pt secondaries and 421 vdc on the plates. Much better. I now have -47 vdc on the bias swinging up to -70 vdc.
So I need to adjust the 220K bias range resistor upwards a little, to like 250K. What a difference a couple of power tubes and some current make.
This is good. You likely already know you'll still need to reconfigure your filter caps for the full unloaded voltage (over 600vdc).
I think I had forgotten zeners need a current drawn to activate their voltage drop. It was silly for me to forget that, since VR tubes (0C3, 5651, etc) must have a minimum current drawn through them to establish their drop voltage as well; these things are a vacuum-equivalent of a zener.
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Thanks for sticking with me HPB - OK I discovered some serious mistakes. First, using Paul Ruby's guide I discovered that the PI plate load resistors and the PI coupling caps were swapped in their positions on the layout, which I have corrected. Hope the caps weren't damaged. Second, all the pots are wired with reverse rotation for a Marshall type chassis, tubes up.. So I've got some work to do to correct that... meanwhile.....
The amp works, although I'm sure this isn't what it's supposed to sound like. The Baldwin OT has two taps, 8 and 16 ohm. I have the 27K feedback resistor connected to the 8 ohm tap, which is pretty heavy feedback ala JTM-45. The amp has a real raspy sound and has a sort of blossoming and fading type thing going on. It does not get very loud. Should be a lot louder so there is a volume issue too. The bias is at -49v.
With a 5U4GB installed (Zener removed) the voltages on the power rail are (A) 375 (B) 343 (C) 311 (D) 235. I am surprised at this and was not expecting the voltages to come down so much. That big choke is really dropping some volts. The (D) node is too low because I have an 18K 3W on that node as I am waiting for a 10K 3W to arrive. It looks like I need to procure a GZ34 rectifier. I could use some diodes in the meantime to rectify and see how it works with higher voltages, and the voltages would be pretty near normal for a 5f6a I would think.
I'll get the pot wiring squared away for now.
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I redid some things and changed all the components to exactly like Hoffmans layout except for the PS rail. Pots wired up right. Went over the voltages compared to what some others have posted and every thing looks kosher to me. Still FLABBY after about 2 on the volume pots. Tried a set of 5881s checked and rechecked bias.. still flabby as heck. I am tending to think the OT is shot. Is it possible the OT is breaking down under load?
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Temporarily installed a brand new Super R OT and it sounded exactly the same. Distorted flabby nasty sounding weird decay on notes especially bass notes. Has lots of power just sounds terrible. Definitely not normal. Reconnected original OT. Will install 2x100uf caps for first filter node with bleeders. Guess the problem is on the board somewhere.
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Hello, I thought I would update this thread with the results, in case anyone else decides to make a bassman or similar out of a Baldwin Orgasonic' iron and chassis.
I finally got a 10k 2 watt resistor on the D power node. And I installed a 12AY7 and 5AR4 rectifier as required. Also, since the power rail can surge on start-up to well over 525 volts, I wired up the
first stage of capacitance (reservoir) like on a Super Reverb, and installed a standby switch. I uses two 100uf 450 volt caps in series to ground with the 220K bleeder resistors.
When turned on to standby the reservoir caps take appx. 10 seconds to charge up and settle, and I suppose this is due to the very large input inductor. When turned on I get
A= 400v B= 395v C=355v and D=300v on the power rail and even though these voltages are somewhat lower than on a real 5F6A the amp sounds pretty darn good. I have it
biased at -45v and running two 5881's at this time.
I think overall this has been a successful conversion.
I'd like to thank Sluckey and HPB and all others for the assistance.
~All the best to you folks.