Vibrato Line Box Caps

[Bobmann]

I am working on a 1940's vintage CV.
I am not really familiar with electronics design and application.

I typically see all the caps in the line box as all the same value on organs I have worked on before, especially on the later models. This one has the following: (all UF)
.00067
.00075
.00125
.002
.0025
.003
.0035
.009
.0147

The question is, are all those values really necessary?
The tolerances of caps cannot be better than +/- 20%, back then it may have been wider than that, so I would think that a .003 and .0035 would not make any difference in any case.

All these values are not available anymore, so how far can I stray from those values?

Bob

PS: Interesting story on this organ. It was donated to a church near here by a couple back in 1944, where it has sat since then.
The couple is renewing their vows on their 75th anniversary and wanted the organ to play just as it did back then.
This is a pretty special rebuild for me.

[tpappano]

IMHO, if you keep your replacement caps +/- 10% of the specified values you should be in good shape. But, if you are obsessive, you can usually parallel two 'standard' values to come up with an oddball value (or damn close)

original: if original value not available you could use:
.00067 .00068
.00075 .00082
.00125 .0012
.002 .0018 or .0022
.0025 .0024 or .0027
.003 .0027 or .0033
.0035 .0033, .0036 or .0039
.009 .0082, .0091 or .01
.0147 .015

A few of your original caps are 'standard' values, but might not be commonly stocked.

My line box used all .004 (non-standard) so I used .0022 and .0018 (common) in parallel.

[Bobmann]

Thanks for the reply.
My ignorance of electrical circuits is phenonimal, so bear with me.

I wonder, however, why it is that other CV line boxes that I have worked on of the same physical size and configuration use all .0039uf.
Later boxes,although smaller in size use all .0056uf.
Is there something in the coils that is different?
Are these devices so precise in operation that using a .002uf or .0025uf makes a difference in the sound?

Also this line box uses 1 watt resistors, which is way overkill, I would imagine.

Bob

[tpappano]

You're welcome! I haven't looked at an early schematic but I'm going to guess that the early vibrato circuit might have been a little over-designed, like maybe a little extra-precise. Perhaps Hammond found he could reduce parts count, cost, etc. by fiddling with the delay line design to use all the same size caps and/or inductors. In theory, going to .0056 instead of .0039 suggests that the inductors would need fewer turns of wire for the same effect, making the coils cheaper and/or faster to make. I do a similar thing with my designs, minimizing the number of different value resistors and capacitors makes things easier to build 8) True on the 1 watt resistors- back then that was about as small as a resistor could be made!

[muckelroy]

I know the V era saw a number of variations in the line box design. 5 maybe - I could be wrong.

Here is my 1945 CV line box innards with roughly the same values as yours, as well as those 1 watters. The resistors are overkill, but for a restoration I’d use whatever size can fit. 1/2 watt carbon comp would look best but I’d prefer a more modern material resistor for noise considerations. You might need to buy 1 watt metal film or metal oxide resistors, for example. Whatever has the beefiest leads to reach the lugs.

[David Anderson]

Hi Bob,

The CV line box was one of the most complicated Hammond produced. 1944 is very early for a CV, so we're in prototype territory here. What's the serial number? The service manual states that there was only one line box for all V-series organs, but it is sometimes the case in very early production, that you find some experiments that get sold as finished products. (This has been found in some Fender amps.)

Most of the caps in the CV line box per the schematic are 2500pF, but you also see 3000pF, 3500pF, 9000pF, and 0.015uF.

As the line boxes grew simpler over time, my speculation would be that Hammond decided that people couldn't hear the difference.

But I can't account for what you found other than it could have been a prototype or experiment. I know that you know what original construction looks like

I guess we should keep in mind that scanner vibrato/chorus was brand new, and they may have been nervous about how it would accepted in place of the chorus generator.

- - - Updated - - -

1/2 watt carbon comp would look best but I’d prefer a more modern material resistor for noise considerations.

There is no mechanism for carbon composition resistors to cause noise in the line box circuit because there's no constant DC current through them.

Carbon composition resistors can only be noise sources in specific circuit positions like plate resistors.

That said, CC resistors are more expensive these days, so I don't think there's a reason to use them here.

[muckelroy]

Mine is serial number 12113 which would have been the 861st CV made. It has cap values similar to what Bobmann has, though I’m uncertain of layout or quantity.

[tpappano]

How many of each value cap are needed? There is a parts house here that has a lot of surplus parts and I would be happy to root through them to come up with a kit of caps to do the rebuild. For some weird reason I like to rebuild old equipment with 'new old stock' that I can lay hands on quickly, even though it only takes 24 hours to get new ones from one of my suppliers, go figure 8)

I like the whole anniversary story!

[Bobmann]

Hi Bob,

The CV line box was one of the most complicated Hammond produced. 1944 is very early for a CV, so we're in prototype territory here. What's the serial number? The service manual states that there was only one line box for all V-series organs, but it is sometimes the case in very early production, that you find some experiments that get sold as finished products. (This has been found in some Fender amps.)

Most of the caps in the CV line box per the schematic are 2500pF, but you also see 3000pF, 3500pF, 9000pF, and 0.015uF.

As the line boxes grew simpler over time, my speculation would be that Hammond decided that people couldn't hear the difference.

But I can't account for what you found other than it could have been a prototype or experiment. I know that you know what original construction looks like

I guess we should keep in mind that scanner vibrato/chorus was brand new, and they may have been nervous about how it would accepted in place of the chorus generator.

- - - Updated - - -



There is no mechanism for carbon composition resistors to cause noise in the line box circuit because there's no constant DC current through them.

Carbon composition resistors can only be noise sources in specific circuit positions like plate resistors.

That said, CC resistors are more expensive these days, so I don't think there's a reason to use them here.

Thanks for the information, David.
This is Serial # 11256.
According to the TWG age list, the first CV was #11252, so this is one of the first off the line.
The dedication plaque on the side is dated October 1944.

The values in this box are not what the schematic calls for.
The vibrato is very choppy, which normally calls for a scanner cleaning. I plan to do this first before touching the line box and see what it sounds like after cleaning. If it sounds OK, I am going to leave it alone.
The owner wanted me to recap the TG based on what they had been told by someone, but after hearing what the organ sounds like I discouraged them from touching it. This is a beautiful sounding organ just as it stands.

Bob

[enor]

In my first CV, I also had choppy vibrato - which turned out to be a break in one of the coils of the delay line.

[David Anderson]

Definitely take pictures and document this one, Bob!

[Bobmann]

I am finished rebuilding the CV.
There were a couple of interesting things other than the cap value issue in the line box.
I checked the values on all the resistors, and they were well within 10% tolerance so I left them.
I replaced the caps with the closest value, which was .0025uf for the .003 and .0035 for example. It sounds just fine.

The scanner stators are made from stainless steel


The music rack base had a hole on the right that was covered with a blank plate. This is where the chorus generator control would be on models that had one. They probably were using up some old stock of parts.


The patch panel was completely populated with screws. I imagine that they stopped doing this later on to cut costs.


The wood used for the pedals is beautiful birds eye maple. It is a shame that these are under foot and not seen.


Cabinet. The hinge and lock is painted brass rather than the shiny brass seen in later consoles.


I am amazed at how great this organ sounds.
My test for need for recapping is by listening to the upper frequency drawbars. Some older organs have virtually no sound from those frequencies. This one I can hear each notch on the very last DB. I am glad they did not insist that I recap this.
I did, however, replace the amp with a Trek unit as requested. They will be replacing the HR40 that they have now and hooking to a Leslie 122. The Trek will simplify this hookup.
This organ will be here for another 50 years, and still sound glorious!

Bob

[Jaim]

Nicely done Bob. Great looking organ.

[carioca100]

WOW Bob, that is a beautiful organ. Can't believe its that old. Those pedals are perfect and that birds eye maple is really pretty. Would love to hear it. Great job and I'm sure that couple that is celebrating their years together will enjoy! Long live that beauty!!

[David Anderson]

Great job, Bob!

FWIW, Hammond kept putting music rack bases with chorus drawbar holes covered by blank plates in organs until ~1947. Either they had a lot of unused stock left over, or they were concerned that they might have to retrofit chorus generators should customers decide they didn't like line box vibrato/chorus. The generator shelves also typically have holes for mounting a chorus generator.

We may never know the reason.