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Discussion Starter #1 (Edited)
I am getting into my 66 YBA1 serial 421 - felt pen or 768 - Label.
I have some questions for those tweakers out there. and Thanks for the Kevin O'Connor Book recommendation to Scottone, that book is helping me get my head around this amp.


So far I found it biased for El-34 with 6L6GC installed, an input wire brushing a B+ wire causing hum and a strange microphonic

I added 1 meg pots a bias cct and removed an extraneous resistor on the presence cct . I have also added a 3 condutor power plug socket.

Next I need to chase down an oscillation when the presence and treble are dialled up. I think I will change out the electrolytic power supply caps as a first attempt to fix that.

My question is about "grid stoppers" I see from later YBA 1 - 4, designs the power tube grids have 1K5 with a Feed of 68K verses the '66 design of 470K feed with no grid stopper.

Is this mod worth doing?
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Telemark said:
I am getting into my 66 YBA1 serial 421 - felt pen or 768 - Label.
I have some questions for those tweakers out there. and Thanks for the Kevin O'Connor Book recommendation to Scottone, that book is helping me get my head around this amp.


So far I found it biased for El-34 with 6L6GC installed, an input wire brushing a B+ wire causing hum and a strange microphonic

I added 1 meg pots a bias cct and removed an extraneous resistor on the presence cct . I have also added a 3 condutor power plug socket.

Next I need to chase down an oscillation when the presence and treble are dialled up. I think I will change out the electrolytic power supply caps as a first attempt to fix that.

My question is about "grid stoppers" I see from later YBA 1 - 4, designs the power tube grids have 1K5 with a Feed of 68K verses the '66 design of 470K feed with no grid stopper.

Is this mod worth doing?
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one side of your heater wiring seems to be disconnected at v1.

Obviously the amp has been completely re-wired at some point and a new output transformer installed. The splices on the OT tranformer should be covered with heat shrink tubing as opposed to black electrical tape.

The oscillation may be pre-amp tube related...have you tried swapping them yet. You could try installing the grid stoppers as they are meant to suppress oscillation at higher frequencies.

I like to see the heater wiring raised a bit higher over the other wiring as well...it looks a bit tight to the chassis in the picture.

Looks like a fun project...
 

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Discussion Starter #3
Thanks Scott, I did fix the heater wiring as it busted off while I was poking around.:oops:

I wondered about the OPT. The previous owner is a tech and freind of mine and was teaching himself about tube ccts with this amp. He found the the OPT miswired and set it up as is.

Yah it's not pristine, but that opens the doors for me and my soldering iron.:banana:

I have changed the tubes with others I have laying around.

Any suggestions for getting rid of the humm?
When it was biased for around 22ma there was no hum, It didn't sound very good ! No it's around 80ma and the idle
hum is substantial.

I may try a bias balance.
:rockon2:
 

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Telemark said:
Any suggestions for getting rid of the humm?
When it was biased for around 22ma there was no hum, It didn't sound very good ! No it's around 80ma and the idle
hum is substantial.

I may try a bias balance.
:rockon2:
Make sure that the heater wiring on the output sockets is "in phase" (i.e. pin 2 of one power tube is connected to pin 2 of the other power tube and pin 7 is connected to pin 7)

Also, if the power tubes are wildly unmatched it can cause excessive residual hum.
 

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Discussion Starter #5
Make sure that the heater wiring on the output sockets is "in phase" (i.e. pin 2 of one power tube is connected to pin 2 of the other power tube and pin 7 is connected to pin 7)
i never would of that of that , makes sense thanks:banana:

-just checked - in phase but not very tightly wound and as you mentioned not dressed very well. I'll see how is sounds after changing the PS Filter caps.:DevilGuitar:
 

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Discussion Starter #7
I can take one later but It is a Hammond 1664, I can't find any info on the Net.

From the wiring it looks as though the choke was also replaced. there is a splice heading to the Powertubes and the soldering on the caps looks pretty messy.

The PT has a Yorkville copper plate with the same serial number as the chassis so I think it's original.
 

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Discussion Starter #8
YBA Transformers

Scottone - The Output Transformer



and the big iron line up!



:rockon:
 

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Telemark said:
Scottone - The Output Transformer



and the big iron line up!



:rockon:
Thanks...I strongly suspect that this isn't the original tranny, but is the same size as the original and same manufacturer. Looks like a lot of rust on the laminates, which isn't a good thing. The choke looks right, but it could have been swapped in from another amp.

I find it strange that there are the two bright yellow wires coming out of the tranformer for the primary connections (they should be brown and green). I can see the brown and green wires in the bundle at the back of the amp, and I worry that these yellow rascals were badly spliced somewhere.

I don't want to make more work for you, but I think you should disconnect the output transformer and remove it to have a look. Something just doesn't look right here.

Might also be a good opportunity to put up a wanted ad for an original Bassmaster output tranny. I know that a lot of folks switch these out for premium units (i.e. Mercury Mag, OEI, etc., so there must be some kicking around.
 

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Old Hammond info

You might google up House of Jim in Winnipeg. His site has some info on old Hammond OT numbers. He also sells great eyelet boards.

It might mean redoing some splices but I'd be tempted to keep the Hammond, especially if you play some low hard core tunings, like open C.

Bass notes need more iron, which is why bass guitar OT's weigh about a third or so heavier than one for lead guitar. Many "Dime Bag Darryl" players will tune below standard pitch and then wonder why their SLO100 or Booger seems to crap out, especially on the lowest strings. The problem is that their OT just isn't beefy enough.

Hammond 1600 series are hifi rated down to maybe 20hz. They keep up just fine!

They are harder to saturate, but if you just play louder and louder... :)

Wild Bill
 
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Wild Bill said:
You might google up House of Jim in Winnipeg. His site has some info on old Hammond OT numbers. He also sells great eyelet boards.

It might mean redoing some splices but I'd be tempted to keep the Hammond, especially if you play some low hard core tunings, like open C.

Bass notes need more iron, which is why bass guitar OT's weigh about a third or so heavier than one for lead guitar. Many "Dime Bag Darryl" players will tune below standard pitch and then wonder why their SLO100 or Booger seems to crap out, especially on the lowest strings. The problem is that their OT just isn't beefy enough.

Hammond 1600 series are hifi rated down to maybe 20hz. They keep up just fine!

They are harder to saturate, but if you just play louder and louder... :)

Wild Bill
Wild Bill, wouldn't you have some concerns with the amount of rust on the laminates? It looks like it sat in a damp basement for about 20 years.

It actually may be a good transformer, but I'm really suspicious about the yellow wires that have been spliced in somehow. If you look at the earlier under chassis shot, you can see the original red, green, and brown wires coming out of the other hole and bundled up at the back of the amp.
 

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Discussion Starter #12
I'm gonna take it apart tommorrow, The rust isn't as bad as the picture showed. Under flourescent lights you have to look pretty close and there is still paint with a _rust colored_ coating. though there is a least one good dime sized spot. ( It probably has spent some time neglected, it was given to my 15 yrs ago and I let it sit for 3 or 4 years, gave away and finally got it back last year. )

I'll see if I can figure out primary, secondary and Taps, it should be interesting.

I have scoped the outuput and it was symetrical, - pushing 40 watts across 8 ohms before it started to distort visibly.


And about Drop C - I am playing a Vince Gill song in a cover band, but the singer hasn't the range so Drop C it is! doesn't quite sound rite onthe YVC-50.
I did some jammin on this amp allready in drop D and it was very good, I will be keeping this tranny if it all works out.
 

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Rust on those old tranny's really isn't an issue. They are so well sealed and gooped inside the rust very seldom gets inside to do any damage. I've seen tranny's so rusty it isn't even funny and they function fine. Alot of the old hammonds have a sepia/rust coloured undercoat on them. Check your ground connections and your wire dress, those are two of the things that just looking at the pictures jump out at me.

Jim from the House of Jim is a good guy and is always willing to help. If you need a tranny let me know what you are looking for, I might have one in my stash.

Ripper
 

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Telemark said:
I'm gonna take it apart tommorrow, The rust isn't as bad as the picture showed. Under flourescent lights you have to look pretty close and there is still paint with a _rust colored_ coating. though there is a least one good dime sized spot. ( It probably has spent some time neglected, it was given to my 15 yrs ago and I let it sit for 3 or 4 years, gave away and finally got it back last year. )
sounds like it's in better shape than it looks in the photo.

The primary should have a red, green, and brown wire, and I beleive the secondary is black and yellow if it's only one impedence tap.

I'm not sure where those bright colored yellow wires are soldered in (the one's that go to the power tubes and the speaker jack). You may have to remove the bell covers on the transformer to find out.

Let us know what you find...
 

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Colour codes...

Scottone said:
sounds like it's in better shape than it looks in the photo.

The primary should have a red, green, and brown wire, and I beleive the secondary is black and yellow if it's only one impedence tap.

I'm not sure where those bright colored yellow wires are soldered in (the one's that go to the power tubes and the speaker jack). You may have to remove the bell covers on the transformer to find out.

Let us know what you find...
There was an industry standard colour code for trannies since the heyday of
Charlie Chaplin. With an OT, the plate wires are blue and brown and the CT is red. The speaker side has black for the common, grn for 4 ohms, ylw for 8 ohms and my memory stalls out about there.

Power trannies have black for the primary, with white or a white stripe for a different line voltage tap. 5v filaments for a rectifier tube are yellow, 6.3v for most tubes are green, HV is red and if there's a CT it's red with a yellow stripe.

Hammond always followed the industry colour conventions. Many guitar amp trannies have oddball colours, especially Marshall. I have absolutely no idea why, except maybe as an attempt to confuse non-factory servicemen.
 

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Discussion Starter #16 (Edited)
Wow

I had hoped to flush some good info out and you guys have delivered Thanks a lot.

I pulled the OPT - the speaker connections fell off when the iron touched the joint:eek: Then the taped splices disentegrated, but at least they were a solid connection.

The Output tube connections were originally Brown and Green, spliced to them now. Yellow.

There was an industry standard colour code for trannies since the heyday of
Charlie Chaplin. With an OT, the plate wires are blue and brown and the CT is red. The speaker side has black for the common, grn for 4 ohms, ylw for 8 ohms and my memory stalls out about there.
I find the Primary to Be Yellow/ Yellow and Red

The Secondary is Black / Yellow- It was wired for 8 ohms, and taped off are, white, brown, green, striped red/ yellow, striped blue yellow. Lotsa options!

Thanks for the House of Jim info: from his site I have the option of 4-8-15-250 or 500ohms! woohoo. SO now I can power that wall of 4-12's if I just wire them in Series!:banana:

more importanly 3800ohms Ct primary and 60 watts audio.

The Color code is only partly legible: It seems to say one of the primary yellow wires should be blue!
and the secondary 8 ohm is black brown!

Except that leaves me with a mystery secondary wire the yellow!:food-smiley-004: This is making me hungry.



 

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I've never encountered an OT transformer with the 2 plate windings being the same color.

At this point (assuming you want to use this O/T), just get some wire of the same guage and attach extentions to these leads. I was taught to do this as follows:

1. strip about 1/2 " of the end of the two wires to be joined
2. twist the 2 stripped ends together as tightly as possible
3. solder the connection
4. cover the splice with heat shrink tubing. 2 layers may be better if possible.

maybe one of the "real" techs can chime in here if I'm misleading you :D
 

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Discussion Starter #18
Thanks Scott, I am going to stick with this transformer pending one important item. It looks like the current might be limited to 100 ma.

a new Hammond 1650N - reccomended for this amp by London Power has a current rating of 380ma.

I'm not sure if I'm miss reading this number or if this will even matter. Anyone care to enlighten me?
 

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Telemark said:
Thanks Scott, I am going to stick with this transformer pending one important item. It looks like the current might be limited to 100 ma.

a new Hammond 1650N - reccomended for this amp by London Power has a current rating of 380ma.

I'm not sure if I'm miss reading this number or if this will even matter. Anyone care to enlighten me?
I took the liberty of putting an ad up on a local bulletin board and found a guy who has a complete transformer set for a 60's YBA-1. Shoot me an email if you are interested in the output tranny.

[email protected]
 

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"As always, it ain't that simple..."

Telemark said:
Thanks Scott, I am going to stick with this transformer pending one important item. It looks like the current might be limited to 100 ma.

a new Hammond 1650N - reccomended for this amp by London Power has a current rating of 380ma.

I'm not sure if I'm miss reading this number or if this will even matter. Anyone care to enlighten me?
We need to nail down a few more factors. That 100 ma rating without more specifics is like a one-armed fisherman showing us the size of the fish that got away! :)

First off, transformers can't limit current. Current is drawn and not pushed. What that rating means is that you should keep the AVERAGE current less than 100 ma, PER SIDE (that is, for each tube in a push-pull circuit) or the transformer will start to get warmer than it should.

Now, the amount of current a 6L6 or whatever will try to draw through the OT winding is dependent on how strongly it's being driven from the preamp/PI stages and by how high a plate voltage is being applied.

Power= volts x plate current in amperes. In the typical class AB1 guitar amp we expect to get maybe a third of that amount in output power, what with circuit efficiency and losses of parts that couple the power. So if the tubes are capable of drawing 150 watts from the power supply (average) then we'd expect to get a max of 50 watts of power into the speaker load.

There's so many factors. The wires inside a transformer might get hot with a strong current load but that's only on signal peaks. On softer parts of the signal or between notes they get a chance to cool down.

Usually designers look at the tube data sheets, which often show all the factors at typical voltages and power levels.

One of the most important factors with Hammond 1600 series OT's is that they are way under-rated and spec'd to deliver full power down to 20 hz. This is far more than an OT in a lead guitar amp would ever have to handle. That's why when you look at the OT in a Traynor bass amp it's much bigger and heavier than in a Marshall or Fender lead amp of equivalent power. It needs that extra iron to handle the energy of bass notes lower than a lead guitar low E and not saturate, which is a condition that adds distortion.

That being said, with a guitar amp we WANT some distortion! So in LEAD guitar applications we can push the hell outta the Hammond ratings. If the 1650N is a 50 watt hifi speaker it will actually sound better as a 100 watt amp OT, or more! There are stories of guys running Hammond OTs so hot you can't keep your hand on the trannie and yet they never burn out...

If your amp ran a pair of EL34s before, then you're talking 60-70 watts of power. I suspect your OT will perform just fine.
 
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