Tubes with SDA?

littlewoodboats

How do the SDA speakers like tube power?

I can get a deal on two of the 50th Anniversary McIntosh MC275's. McIntosh says it is no problem strapping them mono and making common ground.

Tubes hum at low level. Is this at issue with the SDA's lowest registers being done passive? I have read the articles on how the radiators work but do not fully understand.

Schurkey

Good tube amps will work just fine. Some folks will say they're preferable to solid-state.

I'm thinking that if the tubes hum, there may be something wrong with the amp(s).

If your tube amps can be strapped for common-ground, and you can afford that much Macintosh goodness (and you're sure there in usable condition), go for it.

Passive radiators are just another way to vent the cabinet in a tuned manner. The mass and area of the passive driver has certain advantages over a long port.

sda2mike

the hum would be a concern for me.....your 2b's will love the bottle(s)

heiney9

littlewoodboats wrote: »

How do the SDA speakers like tube power?

I can get a deal on two of the 50th Anniversary McIntosh MC275's. McIntosh says it is no problem strapping them mono and making common ground.

Tubes hum at low level. Is this at issue with the SDA's lowest registers being done passive? I have read the articles on how the radiators work but do not fully understand.

Tubes should not 'hum' ever, has nothing to do with SDA's per say. Lot's of people run all models of SDA's with tube gear.

littlewoodboats

This particular Mac goodness had something dropped on them. Dirt cheap and easily repaired. No board damage but one dented chassis. Tubes enough left to properly stock one amp with all questionable. I gave $300.00 for the pair and they were delivered to the house this afternoon.

As much as I hate to agree with the Mac purists the guy that picked the Black and Gold should be beat to death with one.

Every tube set I have ever listened to had some noise on the bottom registers. Track a record at high output and between tracks you can hear the tubes. Back when stereo was just a passing fad all of the mono guys bi-amped and went solid state on the bass to kill the tube noise. Is this not still the case? When I say hum I may have meant something other than what was understood.

heiney9

I have run lots of tubes and heard a fair amount of high powered tube amps and unless they had a problem, they were dead quiet. Hiss is normal if you put your ear up to a tweeter, anything beyond that means there is some sort of issue. Sometimes it's a bad cable, worn tube, dirty tube, unseated tube, bias issue, cold solder joint, mismatched cables, mismatched gear, etc.

When you say "Track a record at high output and between tracks you can hear the tubes" what does that even mean?

Have you even hooked them up yet? Is this what you are getting currently or just going by some old audio lore.

H9

F1nut

Every tube set I have ever listened to had some noise on the bottom registers. Track a record at high output and between tracks you can hear the tubes. Back when stereo was just a passing fad all of the mono guys went solid state on the bass to kill the tube noise. Is this not still the case? When I say hum I may have meant something other than what was understood.

Then every tube set you heard had a problem.

heiney9

Also based solely on the face of your post if you bought a pair of cosmetically damaged MC275's (50th Anniv. ed.) for $300, there's a real good likelyhood there is other damage as well. Probably should have them gone through, unless you are the type of guy that can fully check them out yourself on the proper test gear.

FYI, they sell for $6,500 (each) new retail.

H9

littlewoodboats

Aren't I just the little instigator today? Easy guys.

These belonged to the guys dad and the family never cared. Stacked one on top of the other in cartons they sustained an impact.

I have a good bit of experience with tubes going back to my Navy days. I said there were enough tubes to populate one amp as I have played both of them one at a time.

heiney9

Who's jumping down your throat? No need to tell anyone to go easy. We are all just trying to help.

I'd say you got the deal of the Century. $13,000.00 worth of amps for $300. They are stereo amps so you can run one in stereo. If they are infact the 50th Anniv MC275 like these

http://www.mcintoshlabs.com/us/Products/pages/ProductDetails.aspx?CatId=Amplifiers&ProductId=MC275

H9

nspindel

I spent more on two tubes than I did on my SDA 1C's. With good power, SDA's sing. Tubes make them get up and dance!

littlewoodboats

These are the ones. Gold and Black with a status light system that shed light via leds through the tubes. The purists hated it.

http://www.mcintoshlabs.com/us/Products/pages/ProductDetails.aspx?CatId=Amplifiers&ProductId=MC275LimitedEdition

My question was, how does the radiator work in the lower registers?

heiney9

So you can run one in stereo so you can listen to both speakers at the same time.

If you've read articles on how the PR's work and don't understand it, then I'm not sure what to say.

Here are a couple links to reviews that explain it

http://www.polksda.com/sda1creview.shtml

http://www.polksda.com/srsreview.shtml

H9

littlewoodboats

Thanks for the links. Here is a question for you. The bent chassis unit works perfectly. The bend is bad enough that the board is flexed. The board is grommet mounted.

Would you try to release the board or gently flex the chassis back to spec?

heiney9

It's hard to say without having it in front of me. I would still be worried something is wrong with them if they are that damaged. You have a fraction of their worth in them so if it were me, I'd have them professionally gone through. It doesn't take much to do damage and if the chassis is that fubar'd I bet there is hidden damage not seen by the naked eye. Just going on experience here.

So do both amps "hum"? How does a single amp sound in stereo?

H9

littlewoodboats

They were stacked one on top of the other in boxes. Bad, straight down impact. Top box suffered cage and tube damage. Bottom box looked perfect with chassis deflection noted.

gwg_97

Let's see some pictures of those squished bad boys.

littlewoodboats

I did not take any images but there are a few and will get them.

I took them to a fried who is a pretty good tech though not an audio specialist. The bent board does have a crack and several of the tube sockets are also cracked. I have enough parts to build one naked unit with a few spares. Gut lucky with the crack as there seems to be only a single trace involved (still working) so can cut and jumper there. The current plan is to hammer out the bent frame and use it for a template to make one from wood. I always thought it would be cool to have a tube amp in a wood case. I am sick that way at times.

As it turns out this deal came to me after he had taken them several places and was told no thanks but no thanks. One dealer wanted more for repair that used ones cost. I found these on the web new for around $3,000 and have found some old adds where they sold around $1,200 to $1,000.

Definitely a project but one worth pursuing. I will post some images once the rebuild begins. In Mac's defense they were well packed in their shippers. No one from Mac thought to test by dropping diesel engine parts on them.

transmaster

Alright this is where I live I have several decades of working of tube equipment. My ham shack is full of vacuum tube gear. We call it hollow state electronics. I have never owned the beautiful Mac' hollow state audio amps but I have listened to enough of them throught the years and they do not hum. I could not find a schematic for the MC275 but the tube compliment tells me it has a solid state power supply. Leaky power transistors can cause this problem, bad filter capacitors is a more likely cause. The 12AT7 is labeled as some sort of voltage regulator check it for leakage, it should not be the problem however. This amp has three power supplies, that is the reason for the three large transformers. The best way to find out just what is causing the problem is the go through it with a Oscilloscope. First off it will tell you what the frequency of the "hum" if it is 60 Hz then you know the power supply is not doing it's job in smoothing out the AC input voltage. A real fiendish thing is AC ripple getting into the heater voltage for the tubes. If you find out it is 60Hz you check the filter capacitors, then the power transistors, Sometimes big multi-tap transformers themselves will hum, a stethoscope will tell if this is the problem. Microphonic tubes, especially if you have the before mention humming transformers, can do this to DX just lightly tap on each tube, I have a little rubber mallet designed to do just this, you will hear noise related to the tapping coming out of the speakers. If you have a a reasonably good knowledge of the care of feeding of hollow state gear rebuilding the power supply would not be a problem as long as you do the job the way McIntosh specifies. The only thing that would give me pause is the transformers if they are humming they need attention as in replacement or rewinding. I would imagine new replacements are going to sell for the current price gold. It should be cheaper to have the originals rewound. Have fun and if this is your first piece of vacuum tube gear welcome to the world of Hollow State electronics.
The only thing that would make the Macintosh more beautiful is using 866 mercury vapor rectifier tubes, they glow blue when in operation.

Oh one more thing if you are stacking these amps make sure you have good chassis grounding between the two, yes a no brainer but you never know :cheesygrin:

Fongolio

Last year I rebuilt an Eico ST-70 (yes same model number as the more famous Dynaco) integrated tube amp. It had some hum issues before I replace every cap and resistor in the unit. Now, no hum. As for how it plays with my SDA-1C's....this unit is producing only about 35 -40 watts rms per channel but man does it make my SDA's sing. Truly incredible. Wide and deep soundstage on any source and plenty loud enough for me. Where it is best is at low listening levels. Still beautifully balanced sound at apartment building levels. I can only imagine how more modern designs with even more power must sound with SDA's.

heiney9

littlewoodboats wrote: »

As it turns out this deal came to me after he had taken them several places and was told no thanks but no thanks. One dealer wanted more for repair that used ones cost. I found these on the web new for around $3,000 and have found some old adds where they sold around $1,200 to $1,000.

Then they aren't the 50th Anniversary MC275's. Those sold for $6000 each new and were a limited run so they wouldn't sell for $1000-1200.

Photo's would confirm, not sure why you haven't posted pics yet.

H9

FTGV

transmaster wrote: »

Alright this is where I live I have several decades of working of tube equipment... This amp has three power supplies, that is the reason for the three large transformers....

Where I live two of those would actually be output not power transformers,an art in which Mac was/is highly accomlished at.

Fongolio

Same on my Eico ST-70. One power and two output transformers.

transmaster

It has always amazed me what you can do with a good vintage tube type Amp. On paper they don't put out that much power but hook them to a good set of speakers and it is glorious.

transmaster

FTGV wrote: »

Where I live two of those would actually be output not power transformers,an art in which Mac was/is highly accomlished at.

I am coming from the world of 1950's transmitters. Viking 1, and 2's, Viking 500, Viking Desk Kilowatt, Collins 32V series, Central Electronics. They all had 3 of what we call power supplies. One for the plate and heater voltage, indicator lights etc, a second is the modulation section, and a third for output. The two of these power supplies are for the output section of the transmitter. Coming forward 45 plus years and circuit design has changed but the basic theory of operation is the same for an Amp.

I remember Robert W. (Bob) Carver really pissing off the Vacuum tube audio amp snobs. He would get some of these people into a listening room, they insisted they could name a tube audio amp by it's sound reproduction quality. Bob Carver confounded all of them using the fabled Sliver 7 amp. By changing the internal phasing he could make that amp sound like any high end tube type amp then in production. Bob was not in good odor the the Vacuum Tube crowd.

littlewoodboats

H9: I have not posted images as I did not think about taking any when they were first here. Both units are at a shop at the moment so it will be a couple of weeks at the earliest before I will be able to lay hands on them again. The guy I bought them from has a couple of images that I have requested but have not received them as of yet. (I doubt it is high on his list of priorities)

The only one I have seen at a dealer could be had for well under the $6,500 list price. From the reading I have done it seems the Mac purists hated pretty much everything about these units. A bit gaudy for my personal tastes but to each his own on that one. The lack of the old style "point to point" wiring seems to be what bothers them the most.

Interesting stuff transmaster. The guy that has them now is an old military radio guy with a fair amount of tube experience so checking everything is high on the list of priorities. Were someone to drop the head from a diesel engine on me I am sure I would make some out of spec noises. My Uncle George would have referred to that as swearing in tongues.

I know an old radio engineer from the Austin area that dates back to the gear you mentioned. He left broadcast engineering and worked for an equalizer/filter company in Austin for a time. Funny you should mention Bob Carver as the pro sound guys were less than impressed with the earlier offerings. That said he would be the first to admit that everything he knows is 30 years out of date.

I am hoping for good things but moving and getting the shop back into production takes priority over everything else.

Thank you for the replies

heiney9

I see. And you are right the Mac purists did dislike them alot so perhaps they haven't retained their value, plus I know other high end gear rarely fetches the MSRP. Get some pics up when you can. We LOVE gear pics.

H9

littlewoodboats

Some of the owner reviews I found have been brutal. Everything from a failed power switch to full on circuit board failures. The media reviews commented on the great sound so I am hopeful. If it all goes bad I got them cheap enough the parts will get my money back.

I am a big fan of naked amplifier pics and will be posting some as soon as things settle down a bit.