WopOnTour
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Thanks for the suggestions Craig. I appreciate your willingness to share your expertise
I really like what your saying which I guess (in a sense) is converting the circuit to be more like the Citation II bias circuitry. Bone stock with 6L6GC there is supposedly .5 volts on the "common" cathode circuit.(I now have a SAMs for this amp) I calculated that to be 150mA which seemed pretty high, and why I was wondering if having both cathodes sharing that circuit was a very good idea. (I presume that would mean 75mA each?) I'll have to pencil in what you are saying and see if I can make sense of it.I've still yet to get this amp through my door, but I'm trying to get my plan together to put it to work with my LaScalas.
Yea, your right though- I believe this to be a very much under-appreciated HK amplifier circa 1960. You dont hear much about it anyway... compared to the slightly older (but more readily available?) Citation series.But the A-260 has a lot of desireable features IMO. The output trannies are certainly not as heavy as the Citations, however they are supposedly a special "grain oriented" high permeability core design that extends the frequency response across 15-30,000Hz at 1 watt (+/- 0.5db) that was "all-new" for 1960. I'm not sure about all the supposed "versatility" of that multi-switched speaker output network though. Just a bit too busy with all the switches, flip-flops and straps. I may just pull all that in favor of conventional banks of WBTs.
I really like the idea of being able to mess around with various tube sets though.And your suggestions will obviously make this amp even more versatile. Besides the classic drivers you suggested I've also got nicely matched quads of Tungsol 5881 and GE 7581A that I'm looking forward to trying out as well. I've been looking for a good deal on a set of WU 350Bs or GEC KT66 but alas it appears they are rare as hen's teeth and worth their weight in gold these days. I've recently watched a few matched pairs on eBay going for $500-600 (and the Western Electrics are just rediculous) http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130070374918&ssPageName=ADME:B:WNA:US:12
I may just try out the Shunguang versions of these just to see what they sound like (for a more reasonable investment)
I also have a spare set of HEXFREDs from my 300B projects that I was thinking of trying as well, hopefully to gain a bit more headroom for the power supply.
Anyways thanks again for the advice Craig, I'll let you know how I make out once I finally get going on it (don't want to jinx it by getting too far ahead of myself while the the amp is still "vulnerable" within the shipping channels) [
] WOT
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Another observation and question for some of the experienced tube amp boys here. I noticed in the schematic (full version attached in the post above) for this amp that the 6L6GCs appear to "share" a 3.3 ohm Cathode resistor. What are the implications of this in a fixed bias push-pull configuration? Is there some sort of "counter" electromotive force that affects each individual cathode's net current to ground between each cycle of the output tube set?
I'm thinking of rewiring these into seperate circuits with fully adjustable bias (not just balancing) Any suggestions on doing this??
Thanks
WOT
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I slip on a nitrile rubber glove when I'm pulling tubes. Not that I'm worried too much about perspiration or oils on my fingers, but because I like the positive grip and tactile feel that allows me to roll the tube out more easily and handle them with less chance of a "whoops. Sure cure for "butter-fingers" [
]WOT
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Excellent point. Good thing our ears can hear what's beyond any measured distortion.Speakerfritz--
Just to be clear in my meaning, I don't discount any sonic effect that might be perceived. But the author made an onbjective claim for lower distortion, which is trivial to measure. It might be that the measure reveals nothing, but the audible tests reveal a big change.I've heard some very impressive ~2% THD amplifiers...
WOT
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Well that's maybe a bit suspicious (considering the large volume of top-notch gear he is offering, mostly at "fair" pricing). I cant see how some of that equipment isnt moving, so maybe it's some sort of scam? I find that unlikely as most of it is pinned at BuyItNow pricing with offers accepted so...
I've been dreaming of those MC-40s, they sure look like they're in nice shape. WOT
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This one looks like it should be in the Klipsch museum
Plus, Check out the guy's OTHER auctions. Assuming it's all legit there's some decent deals on McIntosh, HH Scott and other vintage gear.
Some hobby
WopOnTour
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IMO if your willing to spend THAT kind of $$ on crossover caps, I would take a look at Duelunds or M-Cap Supreme. I cant hear the difference between Solens and Sonicaps- doesnt mean there isnt a difference though, I may just have low band-width [Here is a capacitor question. I am re-capping a pair of B&W speakers (DM3000's - small towers). I can go for Solens at abotu $40 or Sonicaps at about $160. Are the Sonicaps worth 4 times the price?
]WopOnTour
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Craig, I finally found a schematic for this old HK A260 (see attached pdf). Any advice to modify it for 350B? Besides a recap and applying some McShane type "touches" to the power supply I was thinking of providing seperate individual cathode bias resistors (at this point each pair of 6L6GG appears to share R42 and R53) Any suggestions for a rewire to make the bias adjustable? Appreciate any comments/assistance...350B will run fine at 400V on the plates. They are good for 27 watts of idle plate dissipation so they could theoretically run 67mA of plate current at Idle with your plate voltage. The 350B is a really upgraded version of the original 6L6 just short of the 6L6GC spec
WOT
My new baby...
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Hey Flynn
Couldnt help but notice your system profile... [
]What 6L6 based amp are you using? I've recently purchased a vintage Harman Kardon 6L6 amp (12AX7>12AX7>12AU7>12AU7>7247>6L6GCx2) in order to ocasionally make just a little bit more "noise" than my 300B SET.
Do you know what kind of plate voltage and bias currents are you operating at?
What tubeset?
Thanks
WOT
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Thanks Craig, I was hoping someone like you would chime in. [350B will run fine at 400V on the plates. They are good for 27 watts of idle plate dissipation so they could theoretically run 67mA of plate current at Idle with your plate voltage. The 350B is a really upgraded version of the original 6L6 just short of the 6L6GC spec
]After I check this ol'girl out throughly and make sure I want to keep it, I will commence looking at possible mods to facilitate some fun tube rolling. This schematic I have is a lousy copy but when I get a decent original would you mind having a look at it and maybe give me some advice??
Thanks WOT
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Do we have an understanding of what the theroy of operation is?
Well there has been a fair amount of seemingly "decent" research and testing on the subject, most notably from Thomas Goldworthy (aka Mudcat) on the old Audioholics BBSLet see ....
CAT 5 cable in the same sentence with "speaker wire": Bad idea
-Tom
http://www.audioholics.com/techtips/setup/interconnects/DIYSpeakerCablesp1.html
I like what I hear anyways...
WOT
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I'm using some DIY braided "Triple T" CAT5 cables and REALLY like the sound, (compared to lamp cord or regular Monster cable anyways)
The "tricks" are:
a) identifying the 2 "loose" and 2 "tight" twisted pairs within the CAT5 and splitting them between + and -
connecting only ONE strand from each of the 4 UTP twisted pairs in each CAT5 bundle to the + and - c) making sure all of the CAT 5 is exactly the same length (even if it one ends up a bit short due to the braids DO NOT trim the others to match! - go back and "adjust the braids) You might want check/confirm with at least a decent DVOM if available down to 0.01 ohm. You should check with an ohmeter to make sure you didnt get something crossed before soldering anyways.
d) NOT to braid the CAT5 segments too tightly so as not to result in excessive capacitance.(some air-gap in the braid is good- I used some felt pens as air-gap gage pins during braiding process which took about an hour/cable for a 10 footer )
I'd post some pics but I covered mine in TechFlex before I terminated them, so you really cant see much.
You can find more cable DIY info here: http://www.tnt-audio.com/clinica/tweaks.html
HTH WOT
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Well based on the schematics that I've managed to find so far, it runs just a bit "cooler" than the Citation 2 (a good thing IMO) with 400V on the plates and 385V on the screens when using the 6L6GCs. I want to set it up with easily adjustable voltage/bias so I can try various tube sets like the 350B, KT66, KT88, KT90 (like the Leben CS 600 which has a trick switch setup to alter the plate voltages, cathode current and bias voltages).WOT, where does it run the outputs? I've used the same quad of 350B in my Mc30 for a few years now with no problems so far. National Unions.
How do you find the 350B Nationals on the Mac? Enough bottom-end extension??
PS > sorry to the op for the thread jack - lol But I'm pretty sure nobody was able to talk you out of WANTING those 8's! (Seems someone ended up getting them for $2400 or so)
WOT
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Thanks, ol'buckster, although I havnt exactly got my meat-hooks on it yet. (it's being shipped this week) But yes I DO have plans for it and it WILL be played. Once I check it all out and recap it. Managed to find a SAM's for it on eBay- WOTLOL [
]Yea, like they're ready to just LAUNCH right outta there! [
]WOT
Good looking amp.................very affordable, nice deal..................Best of luck with it, more of a purchase that I can understand, are you going to use it or save it?
Here's another pics from the rear, looks clean!
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LOL [
]Yea, like they're ready to just LAUNCH right outta there! [
]Here's another pic from another angle (note:there are supposedly shields for all of the smaller tubes)
WOT
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No, I wish, but too think the Marantz #-series are way over-ratedANYBODY HERE WIN THAT POWER AMP ?????????
But I DID manage to win THIS one though..
1961 Harman Kardon A-260 integrated amplifier
Tube compliment : 2 x 12AX7 > 2 x 12AU7 > 2 x 7247 > 4 x 6L6GC ,
IMO it's kind of a a poor man's MC-240, and the iron is decent but certainly not as substantial as the McIntosh- but I've always been a fan of the lowly 6L6GC "geeetar tube"
(But my ultimate plan is to alter the plate voltage/cathode load to allow it to run either a quad of 350B or maybe KT66s in push pull)
Hope it doesnt need too much work, still need to find a schematic...
WopOnTour
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LOL I get ya...Hmmmm
Not sure why the pic doesnt appear...
Maybe try right click and select "Show Picture" ... seems to work for me!
Here's the original URL
http://www.enjoythemusic.com/magazine/equipment/0303/boylan/MarantzProjectT1.jpg
WOT
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I wonder how much $$ a pair of THESE T1's will eventually go for on eBay (someday) ... [
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3Dzapper
I think you misread my question.I'm not looking for transformers- I'm looking for the cover cans to go over the transformers to dress things up a bit
Rigma
I like what you did with the second "finish" plate with your amp. Hiding all the socket screws is a nice touch. I guess you had to router the chassis a little deeper so it ended up "flush" to the top? Also, what schematics did you use to create the mono-block amps? Looks like maybe JE Labs 6sn7>300B (I built the integrated version 76>5692>300B )
Great sounding SET for very little $$ IMO [
]Regards WOT
Speaking of that, has any of the DIYers here ever found a decent source for metal cover cans for their trannies??In something as fancy as that, I'm surprised the transformer is exposed?
(I've just made my own with various materials which is a royal PITA!)
WOT
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I dont think it's anywhere near overloaded as there's only 3 loads connected to it
1 - JEL 300B SET Integrated amp
1- Carver C1 Pre-Amp
1- Thorens TD-800 series Turntable
I doubt that I'm even at 1/2 of the transformer's rated (contiuous) wattage of 750W Although I must admit I've never measured it, but I'll try what you suggest
Thanks
WOT
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I too have bad power with a lot of sags/spikes, brownouts etc (I cant even keep light bulbs to last much more than a few weeks) The power company says it's "as good as it gets"
An audio buddy suggested I try an isolation transformer, so I purchased a Hammond 171F ($166) which is good to 750 watts of equipment consumption (they also make a 1000 watter)
http://www.hammondmfg.com/171.htm
It definately helped a lot but it's still not perfect (I think the transformer itself may be contributing some of it's own 60Hz hum)
I was thinking of adding a filter in the cable, any suggestions?
Fritz would your filter schematic apply to this? (got a part number for the diodes?)
WOT
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connecting only ONE strand from each of the 4 UTP twisted pairs in each CAT5 bundle to the + and - 
GOOD GOD, SOMEONE TALK ME OUT OF THIS ONE....
in 2-Channel Home Audio
Posted
LOL, Yes very [Y]