Leslie amp output tube cathode oddity.

[bigsbybender]

I'm building a Leslie 147 style power amp. It's pretty simple since there isn't a preamp (as it's either in the Organ/keyboard or in an external pedal preamp). I'm using solid state motor controls so I didn't need to put anything in the amp other than audio components, so I decided to simplify the schematic to eliminate what I didn't need. As I was editing the schematic for my purposes I noticed that it appears the speaker leads are tied to the cathodes of the 6550 Power and there is a center tap on the secondaries of the output transformer where the cathode Resistor/Capacitor is located. What is the purpose of this?

  I'm guessing it puts 20-30volts DC on the speakers which wouldn't do anything, so there must be some AC flyback....would this be a type of Negative Feedback setup?

I've planned on using Guitar amp (Marshall-style) iron that I have on hand which does not have a secondary center tap. It just has common 4,8,16 ohm taps.
So if I simply connect the cathodes through the Resistor/Capacitor to ground and connect the speakers to the secondary leads, would I make the amp that much different? Also would I have to recalculate the cathode resistor?

Posted below is my modified schematic.

[stratele52]

is a center tap on the secondaries of the output transformer where the cathode Resistor/Capacitor is located. What is the purpose of this?

Answer ; fisrt time I see that . It is for output tubes bias


So if I simply connect the cathodes through the Resistor/Capacitor to ground and connect the speakers to the secondary leads, would I make the amp that much different? Also would I have to recalculate the cathode resistor?

You can do that.
Calthode resistor ? Yes you must check bias to be sure.

[6G6]

I would try to avoid any DC on the speakers.
The least it can do is cause heat in the VCs,
which you don't want.

[sluckey]

would this be a type of Negative Feedback setup?

yes

I would try to avoid any DC on the speakers.

That's just a 'floating' dc voltage as far as the speaker is concerned. The speaker is not connected to ground, so no dc current actually flows thru the voice coil.

[PRR]

> a type of Negative Feedback setup?

Yes. Works good. Leave it alone.

> 20-30volts DC on the speakers which wouldn't do anything

On *both* leads.

It does no harm (as long as the speaker leads do not get grounded: do not use a metal jack, and prefer an honest 2-pin jack).

The DC voltage -across- the speaker is negligible. First: because it is nominally the same both sides. Also: because the DC resistance of the secondary is very low, under 1 ohm. Nominal combined cathode current is 0.166A. Say one tube quits, the other may draw 0.1A. Through half the winding, 0.5 ohms. We have 0.05 Volts DC in the speaker. Speakers can easily handle DC voltage 1/10th of their Audio rating. 40 Watts in 8 ohms is 17V. It can take 1V for decades, and 0.1V more than forever, 0.05V is quite negligible.

> using Guitar amp (Marshall-style) iron ... So if I simply connect the cathodes through the Resistor/Capacitor to ground and connect the speakers to the secondary leads, would I make the amp that much different?

IMHO, yes. It becomes a vicious Marshall instead of a mellow Leslie. Actually, most Marshalls had gobs of NFB (a different way), so it becomes something else. (Ampeg VT-40? Had no NFB.)

The bias and power would stay the same.

If the original OT is just not available, you "could" wire the 0-4-8-16 winding with "4" to the cathode resistor, "0" and "16" to the 6550 cathodes. (Yes, 4 is the CT of 16.) There's a popular mod for Dynaco which does this. Again you want honest 2-pin speaker connector not grounded-sleeve 1/4" plug.

[bigsbybender]

IMHO, yes. It becomes a vicious Marshall instead of a mellow Leslie.

I have considered that...but for rock organ, that may not be a terrible thing.

If the original OT is just not available, you "could" wire the 0-4-8-16 winding with "4" to the cathode resistor, "0" and "16" to the 6550 cathodes. (Yes, 4 is the CT of 16.)

That may work then....  On the other hand I did find that Triode Electronics have a Leslie style OT for a not too unreasonable $60. In fact that makes the iron cheaper than the pair of new 6550. That would be a first where I spent more for new tubes than new iron.

I'll have to mull this over... I have Marshall iron and a compatible OT, which saves me money....but if I want to do it 'right' maybe I'll splurge for the Leslie-specific iron.

j.

[HotBluePlates]

See if you can find out the mounting footprint of the Leslie-specific transformer (just ask Triode if they don't post it on their website).

Maybe you can get the thing built with the Marshall transformer, then if you're convinced something's missing/not right, you can drop in the correct transformer.

[Ritchie200]

You've got to ask yourself, "Do I wanna sound like Jon Lord, or Jerry Burke (Lawrence Welk) - well, do ya punk?!?"

You already use the wrong wang bar, don't completely disappoint me here....  Search your feelings, you know it to be true...

Yer pal and conscience,
Jim


Jon Lord talks about his Hammond organ sound

[smackoj]

I believe all of the trannys avail. at the Triode Store have a clickable "Specs." button in the description that takes you to a nice draft quality drawing with all the dimensions.

[HotBluePlates]

Well, Jon is talking about *not* using the Leslie and its power amp. He describes tapping signal from the organ and feeding that to a guitar amp.

[bigsbybender]

Yup, and I already made an L-pad to tap off my Hammond's really hot preamp to run it into a Marshall. I got the design from the same guy that actually did Jon Lord's, thanks to Ritchie200 pointing me in the right direction.

What I have is a Leslie from the 1990's with a solid state amp that sounds cruddy.. It stays clean pretty well through the volume range but when it begins to distort, the distortion in nasty and unmusical. Not like the smooth overdrive of a classic tube Leslie. (Think of the screaming Organ tone on old Steppenwolf and early Santana records.)

Maybe you can get the thing built with the Marshall transformer, then if you're convinced something's missing/not right, you can drop in the correct transformer.

I think I'm going to take HBP's advice and try the Marshall PT. (Which I may have bought from him if memory serves.)

j.

[HotBluePlates]

That would've been a hot minute ago...  Maybe in 2005-2006?

Oh well, I've got transformers I've been meaning to use since 1998 and still haven't gotten around to it.

[darryl]

Oh well, I've got transformers I've been meaning to use since 1998 and still haven't gotten around to it.

I still have unused transformers from my previous amp-building business, which ceased production in 1982.

One day I will get around to using them . . .

[bigsbybender]

That would've been a hot minute ago...  Maybe in 2005-2006?

Would have to have been like late '06 when I moved back to the US. I've been mainly building lower wattage amps like 5E3 and Marshall 18watt... The bigger iron has been on the backburner.

j.

[Ritchie200]

Hey Bigsby,

After the 1970-73 Marshall Major into Marshall PA cabinets with horns, I think Jon got tired of the one-dimensional sonic assault.  From the Burn album up to the split, he was using a Crown DC300 (then 300A) into a Leslie with a JBL 2482 horn and Gauss 5840 woofer.  This was basically true reproduction of the Hammond preamp grunt.  It was a little more refined sound with the Leslie whirl.  When they reformed for Perfect Strangers he had a fantastic tone.  That was a "modified" 2203 into the above Leslie.  Not sure what the modification was, unless it was to tame the 50 ohm 3-5v output from the Hammond preamp.  The organ intro on Perfect Strangers is AWESOME!  So, I would say, to quote PRR, go for the "vicious Marshall"!

Jim

The classic MKII blunt instrument assault (still my fav, maybe its a guitar player thing!). Man they were SO good.:
Deep Purple - Lazy (Made in Japan) HD

Here is the Burn tone:
Deep Purple - You Fool No One part1 HD 1974 (Live in California)

Perfect Strangers tone:
Deep Purple - Perfect Strangers

[bigsbybender]

That tone at the beginning of "Perfect Strangers" is what turned me on to them, I'm from the MTV generation so that was my first exposure to Purple. It's also the setup (more or less) that I saw him use at the times that I saw DP live. If memory serves, I first saw them when they were pushing "The Battle Rages On". I did get to see them in '02 on Jon's last tour, which was was great! It didn't have Ritchie but the songs they played were everything you'd want to hear.

Last I saw them was in early '04 when Don Airey had taken over the old C3 Hammond, he was running Twin Leslies but also had some Hughes and Kettner half stacks. Still pretty good tone and although he's not Jon, his rock pedigree is second to none.

j.

[Ritchie200]

I guess I'm partial to the MKII tone because I first saw them in 1972.  That Hammond/ring modulator/Major through those PA speakers was awesome to behold!  I also saw the Perfect Strangers tour, and then a few years ago with Airey.  Yes, Don has to be considered Rock Royalty!  His history is unreal!  Sorry, DP without Ritchie is....NOT DP!  Don't even get me started about Morse...

Interesting story about Jon's C3....  It used to be Christy McVie's.  The story goes that back in the 70's Jon's original Hammond broke down and he needed one quickly.  He was friends with Christy, borrowed hers, and never gave it back!  I'm sure there was some compensation somewhere along the line!  Another interesting tidbit about Jon was he considered George Harrison one of his best friends (they were also neighbors).  They spent quite a bit of time together and Jon was devastated when George died.  George actually appeared on stage with Deep Purple in Australia on the Perfect Strangers tour.  Joining them for their encore, Lucille, George played one of Ritchie's Strats.  Certainly a step up from those Gretch banjos with the weird wang bars that he normally played!

Also, from Burn forward, Jon was running twin Leslies.

Vicious Marshall?

Jim

[Willabe]

Sorry, DP without Ritchie is....NOT DP!  Don't even get me started about Morse...

Didn't Tommy Bolin also log some road time with DP?


              Brad        

[bigsbybender]

Sorry, DP without Ritchie is....NOT DP!  Don't even get me started about Morse...

Didn't Tommy Bolin also log some road time with DP?


              Brad        

Yup, in the Mark IV lineup with Glen Hughes on vocals. It was a mega-talented lineup but drug abuse got the better of Tommy and the problems caused Deep Purple to break up. Tommy died of an overdose just a few months later. His family hosts a regular tribute show/festival in different places Iowa, where they are from. Sometimes former DP members come and join in. A few years back the tribute was where I was living, so I got to go and see Glen Hughes and Ian Paice.

 

[Ritchie200]

Yeah  BB is right.  Hughes was having serious substance abuse issues at that time too.  I also saw that version - not good.  I had seen Tommy when he was with the James Gang after Walsh left, and he was great.  It was a shame.  I have all his solo stuff and also the stuff he did with Billy Cobham on Spectrum - genius!  Funny as I also saw Hughes before DP when he was with Trapeze and then later in the Hughes/Thrall Band.  He also sang on a very good Sabbath album!  So, including Ian Gillan, there were two DP singers that were in Sabbath!

I was hoping for a MKIII reunion as Glenn is clean and singing better than he did in the 70's.  Coverdale sounds very good for his age too.  The only piece missing was stealing away Paicy from the DP MKIVCCV... lineup.  Both Ritchie and Jon had expressed interest.  Years ago in about 1981 Ritchie and Coverdale were trading punches and wrestling on the ground backstage at a Rainbow concert.  Coverdale had always slagged on Rainbow because he never got over Ritchie leaving DP.  Ritchie had had enough and went after him.  Water under the bridge for both nowadays.  Now Jon is gone.  It is so sad that contracts and egos get in the way, and now its too late.  Beatles, etc., etc., etc........  What magic could they have spun if they had made it back into the studio.  Very sad.

Jim

[Willabe]

I had seen Tommy when he was with the James Gang after Walsh left, and he was great.  It was a shame.  I have all his solo stuff and also the stuff he did with Billy Cobham on Spectrum - genius!

Yes! I loved the James Gang/Bolin recordings. What 2 or 3 in total? I saw him not long before he OD. He was playing at the Aragon Ballroom in Chgo. He was on auto pilot and never moved from the mic stand all night after being walked/helped/carried out from back stage (and then off stage) by 2 groupies, 1 on each arm. It was a long time ago (75?) but I seem to remember he played great?

I have his solo stuff and love the Teaser album. If you sit down with the Teaser album and read the lyrics it's clear he was lost, very lost and "if I only knew which way was home there I'd go" point's to it. (I think that's the lyric?) Also the song Dreamer is telling of it too.

Some day I still have to get my hands on a copy of the Billy Cobham album.

I really like the singer on the Bolin/JG albums.

Here's 1 cut I love, Must be Love, Bolin/JG;

(Although I don't consider Tommy a slide player he sounds pretty good on this, the bands rhythm tracks pretty cool/rockin.)  

http://youtu.be/kLy63Pq1rUw

Here's another track I love, Got no time for trouble, Bolin/JG;

(Some nice wha wha at the end of this)

http://youtu.be/OsRox1iTsow

Years ago in about 1981 Ritchie and Coverdale were trading punches and wrestling on the ground backstage at a Rainbow concert.

Well so much for English passivity.      That's why I'm giving up guitar for one of these,             Gonna be a Cajun bluesman. (Jim, I'm gonna need to barrow your Marshall Major for the world wide tour when I make the big time.     )


                  Brad      
 

[Ritchie200]

Do you REALLY want to make this    louder?

Yeah Teaser is great.  My band used to do Wild Dogs.  That and Simple Man were our slow songs!

When Tommy tried out for Purple, he showed up with a "...beautiful Hawaiian girl who was wearing a crochet dress with nothing on under it.  His hair was different colors with feathers in it."  Obviously a nice touch , but also way ahead of his time with the hair!  That and three stacks of Marshall 100 watt super leads and he had the job!  (a pale sonic replacement )


 
Jim

[Willabe]

Do you REALLY want to make this    louder?

In front of 100,000+, night after night, doin "The Funky Blue Crawfish"? Yes!


               Brad