[TheChairGuy]

Bill, you'd be lonely without that l'il red fella'...nuthin' I know of (active preamp-wise)compares for that price. 

[Berndt]

Bill, you'd be lonely without that l'il red fella'...nuthin' I know of (active preamp-wise)compares for that price. 

I have an integrated amp I can use, while you give this one a try and see if you can quantify our earlier results.
I am in between crossovers right now so I'll have some hohum speakers in the interum.

[TheChairGuy]

Well, I changed out the 12AU7's to the originals that came with the amps and things sound a lot better today.

Perhaps that's why I got these 'slightly used' Sylvania's so cheap on ebay a few months ago - they suck (or are old - one or the other, or both).  It's tone certainly has changed to more pleasant, as has explosiveness/dynamics.  It still doesn't make holograpahic images like your little Mapletree does tho, Bill - I KNOW it would be better off with the MapleTree than my Dynaco PAS-4 here.

I'm trying hard to keep audio purchases to a bare minimum.  I issue myself no Xmas bonus' at this time of the year as we have company money tied up in shipments in transit to US for coming Spring now....my income usually spurts in March (I pay myself little each month - most of my income are company profits) when we start getting paid by vendors.  12 years of doing it and it's mostly the same - a few/maybe 3 months of feast, perhaps 5 okay, and 4 lousy.  I'm in the lousy period right now.

If I use your Mapletree, I'll want one    And, I'd rather keep the $850 in the bank right now  Thanks tho, I might take you up on your offer in a few months tho if that's allright.

[Berndt]

Kinda thought that's why you were saying no...
They'll be here when you are ready, or just want to do some a/b'ing.

[TheChairGuy]

I wrung out some further improvements today from the system...'twas good.

The relics actually are rack-able....and originally came with mesh fronts (they didn't make it to me 50-odd years later).  The flanges (you can see pics on page 1) are rack width.  So, I've been racking them one on top of the other.

That turns out to be a no-no - excessive hum is the result as is a certain loss of clarity and stereo separation.  Who knew those big old trannies were such ugly emitters of EMI (well, you DIY and engineering types probably do, but it's quite a revelation to a chairguy  )

Spacing the two amps out by about 2" on the rack (in other words, I propped one up 2" from the other) seemed to improve all aspects of it's performance tonite.  Hooray for the simplest and cheapest of 'tweeks' 

I also tightened down all the screws holding the trannies down.  The sum total of both was a notable reduction in audible hum.

These are pretty generous sized trannies, and plenty old, so I think the slight hum is mostly here to stay (maybe I can buy some silicone washers to dampen it a bit more).  But, now with just a little volume it's no longer noticeable - and it is sounding quite delicious in here. The midrange is tube-a-licious and I note no great deficiency in bass or treble quality or quantity.  In fact, slam is remarkably good - better than I had expected a tube amp in my price range to perform 

These are the best amps I've ever owned (not that my list is exhaustive, or uber-high end in nature).  50 tube watts is more than enough for my room, listening habits and speakers...and because they only put out 225 watts per side I'm able to play them thru the BPT-2 Balanced Power Conditioner and ring additional improvements in sonic texture and noise levels by filtering out common mode noise substantially.

[slbender]

Hi ChairGuy,

Kinda nice lookin' amps... for ugly amps if you ask me. I'd guess that there is a selenium rectifier in the fixed bias circuit in there.  Check that service manual you bought, yup, it kinda looks like it ( the blue square part with two squares ).  I'd worry about that next, they can spontaneously go poof, giving off a spray of <I>Very Toxic</I> stuff into the air, that won't be easy to get rid of.  And then also there go your new semi-expensive output tubes, and maybe the transformer.  Hang a nice 1N4007 or two and a 47 ohm to 150 ohm resistor in series to make the modern equivalent of that rectum-frier.

And good luck with the tube amps.


-Steven L. Bender

Yeo Good Doctor,

I found an old thread from AudioAsylum where a very experienced tuber said the Dukane's are 'really something'.

So, I bought 'em 

I changed out the 6CD6's..man, the old RCA's it came with were tired.  It snapped everything to attention - bass, treble, imaging and more definition...pretty much textbook old tube ailments, I think. I'll swap out the 12au7, OD3 and 5U4's soon, too.  It's not even $100 to do all this...good for another few years.

The 6CD6 is truly weird, my limited reading on the subject indicate that it was a TV tube.

These are 50 watters...and I bought the service manual on ebay too, from another seller.

[TheChairGuy]

Hey Steven,

Thanks for your input 

Yep - it is a selenium rectifier.  I asked my tech on that subject (Scott F had brought it up earlier in the topic) and he said if it goes, we just replace it.  There won't be any damage downstream.  They are for many years a McIntosh service center...so I'd hope the fella' knows his stuff.  Otherwise, I'll ask him to come mask and air sanitizer in hand and clean up my stinking room 

It's a commercial amp (made for PA systems in schools, etc) and parhaps built for the duration.  It doesn't even have on-off switch.

Incidentally, that last bit of 60hz hum was banished by using cheater plugs on the 3 prong cords...it's now as dead silent as any SS amp I've owned.  My speakers are only 87db efficient, but I don't hear anything worth a damn until my ear is 6" from speaker cone. 

Changes/swaps to the 6CD6 output tubes, or rectifier or OD3 Regulator tubes yielded very little change in sonics......but swapping around the 12AU7 input tubes was tremendous.  The cheap Sylvania's I bought on ebay were cheap for a reason - they blow.  I swapped the original hodge-podge of 12AU7's that came with the amp, and it snapped back to it's beaut-ious self 

I've got my eye on some EH 12AU7's (cryo'ed) now.  I have read that they are among the best of the new ones out there, fully competitive with NOS stuff. 

[jt1stcav]

The ONE amplifier I truly regret ever getting rid of, out of so many over the years, was a Magnavox console unit pulled out of one of those big home units of ~1960 vintage, PP 6BQ5/6EU7/5U4. This was, I would say, the best tube amp I have ever heard, and I have heard plenty. Keep us informed on your Journey To Thermionia.

Just read your journey through valve territory, and I'm glad you're liking it all so far. Through all the tube rollin' and cap changes, in the end it's all worth it when your music jumps out at ya and sounds so alive it's scarey.

On the quote above, I just wanted to add that I too had the pleasure of borrowing my bro's '60s vintage Magnavox single-ended pentode 6BQ5 console amp for a time. What a terrific sounding little amp it was...only about 2 or 3 WPC in class-A with two new Ei Elite gold pin 6BQ5s, a single new Electro Harmonix 12AX7EH, and a NOS 1951 Sylvania 5U4G rectifier. It was an ugly duckling of an amp in its simple stamped steel chassis with the same screw-on terminal strip for speaker cables; the original owner gutted the console and cleaned up the amp's chassis, replaced caps, and added a power switch, a fuse, and a new power cord to the mix. And I also agree it was one of the sweetest tube amps I've ever had the pleasure of listening to with my 98.5dB sensitive Klipsch Cornwalls. When my 300B SET amp I had ordered finally arrived, I gave the Maggie back to my bro, who later sold it for a new, more powerful tube amp...kinda wish he had kept it. You just can't beat these ol' classic tube amps IMHO!

[TheChairGuy]

Yeah, the little Dukies are really singing of late.

Most of the tubes in it pretty much neutral as to any sonic betterment...the output tubes, rectifier  and voltage regulators ones, that is.

But the 12AU7 input tubes...boy, do they ever effect the sound.  I bought two matched pairs of Electro-Harmonix12AU7 (cryo'ed) gold pins (two per mono amp) and did they ever improve the proceedings   The 12AU7, as I've read, was originally not intended for hi-fi use...so the NOS jobbies around tend to be a bit too microphonic and noisy for hi-fi.  These EH numbers are made specifically for hi-fi...with low noise and tame microphonics.  The difference is substantial.

I may even try the more linear 12BH7's in those slots as the power transformers are built to overkill specs a can handle their higher 600ma (vs. 300ma for the 12AU7's).

This is a really weird amp as it was most often used for PA purposes.  As such, it has very, very high gain.  It mated poorly with both my old Dynaco PAS-4 and new Quicksilver Full Featured Pre-amp until I learned to dial down the gain settings on the Dukies (they came equipped with gain controls). It was picking up all the noise in the Dukies and I couldn't use but a quarter of the volume control on any pre-amp before deafening levels set in.

Now, the Dukies (with dialed down gain) do what they do best...output immense tube power (but noisily with too much gain) and leave the nuance of lovely pre-amplification to the (quieter) preamp stage.  It's just friggin' beautiful in here now, just beautiful to listen to all day 

[Incredulous]

Just an FYI - there's a pair of similar Dukane amps on eBay right now (I'm not the seller).

http://cgi.ebay.com/Dukane-theatre-p-a-tube-amplifiers_W0QQitemZ320076387948QQihZ011QQcategoryZ73371QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[TheChairGuy]

Hey cool - those are the big brothers to mine, the 1A435B's.  Mine are rated at a very conservative 50 watts...those should be about double that.  They pack a wallop for their ratings I assure you 

I was fortunate to find an original Service Manual for it....there may or not be such around for these models.

Triode Electronics has an online schematic of it, tho, to help you DIY guys...or your technicians:
http://www.triodeel.com/du1a475.gif

These offered seem to need TLC before playing...mine were in working order.  Being positively not a DIY'er, I don't think I would have bought mine were they not in operating condition to start.

These models do not have rca jacks......you need to fashion your own interconnects for them.  Ditto for power cable (no IEC's, you simply connect 3 wires to appropriate places in back of amp) and speaker cable (taps for ground and either 4 or 8 ohm supplied).  I tell you thin as it's not an amp you tweek with such things as cables.  They are set and forget....monkeying around only with tubes (or if you are handy, changing out other parts).

Once working with good tubes, caps and resisters, outfitted with above mentioned cables (and strain-relieved)...you got yourself one humdinger of an amp.  If you're not handy, expect a $500.00++ bill for re-tubing and service work to get the two running right.

Vintage amps bring with them vintage problems....but in this case, a lot of great sound along with it 

[JoshK]

Do you have a schematic of the amp? 

[TheChairGuy]

Do you have a schematic of the amp? 

I have schematic of my amp, the 1A435B.  It came with the service manual. It's kinda' huge, tho, I'd have to go to Kinko's to downsize it or make full size one for you if you want it. Lemme' know.

[JoshK]

I was just thinking I'd look it over see what there was to play with.   

[TheChairGuy]

I was just thinking I'd look it over see what there was to play with.   

Jeez, man - what's your backlog of DIY projects look like already

Felicia must have the patience of Job and the humor of Seinfeld all in one 

[gkargreen]

Just got some of these amps, I would love to get a schematic/service data on these!  Thanks!

[JoshK]

I was just thinking I'd look it over see what there was to play with.   

Jeez, man - what's your backlog of DIY projects look like already

Felicia must have the patience of Job and the humor of Seinfeld all in one 

Its laughably long, and my time to work on them is scarce.  Sometimes I don't even use the time I do have like right now, when I am on the internet.  But I do generally make progress, but it is typically a bit of progress on 3-4 projects at a time, rather than devoted to finishing one.   I always end up finding I am missing a piece to finish the one, so I move on to the next thing while I order that piece and so on.  Or my baffles are drying from being laminated so I can't do anything more on that for now, so I am making a box for my SB PSU. 

I am an unorganized mess. Perfectly chaotic, but I have a method to my madness, quite like a crazed scientist.   I also find that the first part of a project is far more interesting than finishing it.