Jim kelly single channel layout ?

[Synchu]

Thanks for the note. I posted a PM to Colossal.
Niki

[Synchu]

Couple of shots and some rough sounds while still in "design phase". Temporarily soldered components quite evident.
I am waiting for few components to arrive to try few things, prior to post the whole thing in a separate thread, including the schematic and hopefully, at some point - the P2P layout.
But it is the Kelley amp pre (with some changes making it actually closer to Ampeg SB-12 pre) going into Class A, SE poweramp (defeats part of the design goals of the original, but it is becoming quite an interesting amp ). It can use 6V6, 5881, KT77, 6L6GC as a power tube and sounds good and quite different (expected) with all of them. P2P wiring.
[img:500:500]https://farm2.staticflickr.com/1669/263 ... a38850.jpg[/img]
[img:500:500]https://farm2.staticflickr.com/1508/263 ... 6cfbae.jpg[/img]
Sound
https://soundcloud.com/synchu/leftover-something-2

Btw., I verified my build against the layout as kindly made available to me and the layout still seems to be missing the coupling capacitor after V1B.

Niki

[oj]

Btw., I verified my build against the layout as kindly made available to me and the layout still seems to be missing the coupling capacitor after V1B.

Niki

Hi Niki !
That sound odd to me.
I probably have all the schematic and layout that have been on the web, yes they have all errors or are not complete, but I have never seen that they are missing the coupling capacitor after V1B allways been a 10 n on the plate (220k).

[oj]

John Suhr changed the shared screen resistor in 2 X 3K9@5W. There must be a good reason for that.

No that was not John doing that, Jim use 2X 4K/10W on his later models probably to make the 6V6 tubes to last longer.

[oj]

Hi,

Kevin O'Connor featured the two channel amp in TUT vol 5, but with an updated (Super Stock) Power Supply (different from Kelley's original).

After Suhrs involvement and reissue, the website deleted the two channel amp schematics (with voltages); one as originally built and a later version with LED Bias and modifications to the Gain Channel

As originally built, one channel had a 12AT7 tube and the other had a 12AX7 with the signal diodes. The later version had 12AX7's in both channels, the gain channel had removed the signal diodes.

Kelley's concept was to keep the amp clean and let the power tubes supply the distortion, which was contrary to what MESA and Marshall were doing at the time.

Best regards,

Steve

Hi Steve

Well I guess that is my fault that Kevin O'Connor did spend a chapter in TUT5 about Jim Kelly amp, I gave him the schematic I had and info about my experience playing on one.

Yes Kelly did change the two channel amp later on.

Rhythm/clean channel are like u say: 12AT7 to 12AX7 no diodes and the bright cap 470p to 220p.

Lead channel (which had the power attenuator on it)
Kept the diodes but the bypass cap om the cathode went from 20 uF to 2 uF also the slope resistor went from 100K to 220k.

The amp also got a boost cap .0047 on V4A and some minor modes on the reverb, he also change the screen resistor to 2X 4K/10W

[Synchu]

Btw., I verified my build against the layout as kindly made available to me and the layout still seems to be missing the coupling capacitor after V1B.

Niki

Hi Niki !
That sound odd to me.
I probably have all the schematic and layout that have been on the web, yes they have all errors or are not complete, but I have never seen that they are missing the coupling capacitor after V1B allways been a 10 n on the plate (220k).

My bad - it is V1A coupling capacitor that was missing.
It was the schematic that was available on the jimkelleyamplifiers.com web site (it was deleted, but still available through various internet archives).
Niki

[oj]

Btw., I verified my build against the layout as kindly made available to me and the layout still seems to be missing the coupling capacitor after V1B.

Niki

Hi Niki !
That sound odd to me.
I probably have all the schematic and layout that have been on the web, yes they have all errors or are not complete, but I have never seen that they are missing the coupling capacitor after V1B allways been a 10 n on the plate (220k).

My bad - it is V1A coupling capacitor that was missing.
It was the schematic that was available on the jimkelleyamplifiers.com web site (it was deleted, but still available through various internet archives).
Niki

Like Forrest Gump sad : Skit happens

[dorrisant]

I ran a calculator for the PT current draw... I have a Dynaco 4k3 sitting here.

Did I do something wrong? I wasn't expecting the current draw to be that high.

Anyway, looking for a PT that will work for this.

[Synchu]

Nothing wrong with your input.
Just the amount of approximation and assumptions taken when calculating the current draw - factor in hugely when there are large deviations from the datasheets.
See the referenced text from Merlin's web site:
"Even without a load line you can estimate the output power for a typical pentode, assuming the load impedance isn't unusually small for the type of valve being used:
P = 2 * (HT-50)^2 / Rload"
That is exactly what I put in the calculator. One of the assumptions that is usually pretty close to the reality - is how low plate voltage can swing - 50V for a typical PP stage, typical pentode/tetrode operation.
Second important one is "load impedance isn't unusually small" - while ~4k is OK for 4 x 6V6 amp - this is at ~300V plate voltage.
At ~450V this does not hold true (assuming I is the same - albeit it will obivously going to be adjusted, if we don't aim for fancy fireworx ).

At the plate voltages of this amp, I would rather go the standard way using load lines to estimate the maximum current draw, starting with 14W max. power dissipation (which is still higher than the datasheet, but as far as I am aware this is the dissipation that JK amp puts out), 4.3K output impedance and plate voltage of ~450V.
In practice, I would expect that a power transformer between 160mA and 200mA should handle current requirements just fine.

Niki

PS. I am hapilly taking any suggestions for improvement of the calculator

[dorrisant]

Thanks for the explanation Niki, and thanks for the calculator in the first place.

I'm thinking about springing for a 250mA Edcor PT, sounds like it should be adequate then. I have a blank chassis from CEDist that will use. I just can't stop myself from gathering parts... The sickness continues!

[John_P_WI]

Tony, KOC in TUT5 called out a Hammond 273BX (201 ma) in his Kelly chapter if that helps.

John

[dorrisant]

Tony, KOC in TUT5 called out a Hammond 273BX in his Kelly chapter if that helps.

John

Thanks John, I was wondering what he specified for the build... looks like 201mA. No filament tap though. Since I was thinking Edcor and would have to wait for them to build one, I may call and ask if they could add a 60v bias tap to an existing design.

Ok... that about does it for the preliminary build questions, I'm gonna build one as close to exact specs as possible. If any of you see anything I might be missing, please let me know. I will post up a new thread here and probably on rj's site at the same time.

[Synchu]

I am looking forward to it and will follow on. Definitely in my to-build list to do the full blown amp. While the SE experiment, I did and described above turned a very nice small amp, the PA stage of this one is critical to its acclaimed sound properties.
Btw., I like Edcors very much, would love to get some more, but they cost their weight in gold till come to Europe, so will source something more local...
Niki

[dorrisant]

I found and purchased a Stancor P-6314 PT on eBay... shipped cost was about $15 -$20 less than the equivalent rated Edcor and will arrive about 5 weeks earlier.

350-0-350 @200mA
6.3v CT @5.5A
5v @3A

Now I just need to figure out the leads to the Dynaco clone OT again... and order a bunch more parts.

[fenderbender]

I worked on a friend's Fortune amp (Jim Kelley), that thing had a PT that put about 510V on the anodes on the 6V6's, at 120V line AC. I figured Mr. Kelley used a PT intended for 110VAC. I suggested to my buddy, to get a Variac, so he could lower the voltage a little. At 110VAC it sits at about 475VDC on the plates....
That was the single channel non-reverb version. It sounded really nice with and without pedals in front of it and loud as hell!

Tom