The AM Forum

hi Guys, Anybody have specs on an 8005 tube. Can a 811 be put in its place?
We have an old 200w  mac audio amp with a pair and one phase is clipping. Might be a soft tube.

No can't just pop the 811 in there,
8005 has 10v, 3.25a filiament, it also not a zero bias type like the 811, takes about -70v for
class b.
Has about double plate dissapation of 811a, 85 watts..

73, Chuck

TNX Chuck. Our tech found one tube not lit so he removed it and reinstalled it.
It lit right up.  A good reason for clipping. We do need to find a couple spares though.

Rottz o ruck, Frank! They are made of unobtanium. they are really tough to find and usually rather spensive when found. You would be better off to rewire the amp to use 811's or 812's if you dont need full scrote operation. I have an old-buzzard 6' rack transmitter that used them. It took me a couple of years to find a spare pair without having to cut off the left one.
                                                  the Slab Bacon

Yup I see web prices around $130 each.
This is an old MAC amp we use to inject audio on power leads to see if we can shut things down. A pair of them would make a nice stereo. 
Sounds like a job for a pair of 572Bs if we have to modify it. fc

A pair of 572Bs should be able to inject pickled eggplant into the power leads!

But onto the more serious side, I know that K4KYV also has an 8005 rig, he may have a stash of spares..................................

We? Who we be?
Shut what things down??
And why would audio on power leads shut anything down??

When "we" get tired of that amp, "we" here are interested in it... please keep that in mind...

Btw those 8005s got shiny nickel plates??

         _-_-WBear2GCR

Switch mode power supplies sometimes don't like weird stuff on the powerline.  And sometimes analog supplies can pass stuff thru as well.

we be work, no ham fodder will be wasted here.

An 812H would be perfect. Just change out the filament voltage to 7.5.

Gee Huz,
This mac amp in in a small rack with plenty of room inside. I could just mount a variac in the fil transformer primary and tune it to the voltage we want to use. Many people would like to take this amp home when it dies.  tnx for the ideas guys.

Correction, make the fil voltage 6.3 for the 812H.

Hi Frank,

The amp in question here is probably a Macintosh MI-200; the vintage tube audio guys in Japan, Korea, etc., would pay a small fortune for that amp!!! I have a friend who has two of them for his home stereo; they are massive amplifiers that will deliver 200 watts of effortless triode power.

BTW, I think that amp runs the 8005s in class B operation, but I'm not entirely sure of this. I was never too hot for class B tube amplifier operation for home audio applications, but it works for me with a pair of 833As for use in a modulator in a BC or ham rig.

Best Regards,

Bruce, W2XR

Saw one at a hamfest about 15 years ago. Nice amp.

I use a pair of 8005s in pushpull in the rf final of one of my homebrew transmitters, but don't want to part with any of my spares.  I lost one a few months ago when I was working on the transmitter.  It slipped out of my hand and dropped about one foot onto carpeted floor, but the filament wouldn't light afterwards.  I was hyellowfied!  I have one other spare with an intermittent short between filament and grid.  I have never thrown it away, in case I can maybe get it to work in a pinch.  Have 3 good spares left.

One thing I like about those tubes is that they will draw gobs of plate current.  Seem to have loads of reserve emission.

Unfortunately, they have become a hot audiophool item.

Don,
I would never think of taking ham fodder out of action. We will limp along until it dies again then panic.
Corp. America MO. I found a couple on the net for $130.
I think it is a mi200. It is in about a 24 inch rack on casters. The transformers look pretty big.
It has a number of output taps. One plate looks like it has ran hot the other looks ok. When the problem was reported I suggested they swap tubes to see if the clipping changes sides. this is when we they found a tube dark.

I once read somewhere where RCA recommended the 8005 as a replacement for the 203A.  Perhaps this could be reversed; if someone has a supply of 203A's on hand, they could use them to replace the 8005's.  The filament voltage/current is the same.  The sockets are different and instead of a plate cap, the plate lead comes out the socket at the bottom of the 203A.

Even though they are very similar in electrical characteristics and physical appearance (it's just a matter of amplification factor), 203A's have never caught on with the audiophool community to the extent 211/VT4C's have.

TNX for the ideas. I have become the go to guy when it comes to HV and QRO having fixed two amps in the heat of qualification testing. Good to have ideas in the bag of tricks. Tubes are way too magic for these wipper snappers.

AH HA!! thats why we cant find them anymore for our old buzzard transmitters!!  >:( >:(

Other than  the McIntosh MI-200 I am unaware of any other amp that used them!

So, I doubt that Japan has snapped them up in particular.
Also, I have yet to see a project/website/article on an audio amp that uses the 8005.

Don't think they actually made all that many of them - probably a few orders of magnitude less than something like an 811, and another order or two less than the 807...

Besides, I don't think they're such a wonderful tube compared to some others.

       _-_-WBear2GCR

Generally, tubes with plate caps aren't favored by the tubeophiles, especially with plate voltages of 1500 and up.

the audio fools who have plate caps die off quickly because they need to feel the love and contact  " Ready Kilowatt" 

8005s were designed and marketed by RCA for ham use. They never seemed to catch on and they were pricier than their smaller counterparts (811s). I dont think they ever really got popular. I also dont think the military ever used them, hence no slurpuss ones to flood the market. I'm too cheap to pay $130 for them, henceforth, it took me a loooonnnnggggg time to find a spare pair for the W4DEK  old-buzzard 6' black krackle rig that I'm restoring.

I'm sure that there is someone out there that is more familiar with them than I am, but I know that they are not very commonplace.
   
                                                       the Slab Bacon

Hi Frank,

Max is going to see if the tube is in any of the old tube manuals we have. He suggested waliking across the street to the tube museum and see if there is one or two there too. 

You should just locate the units for any price and stick it to the man.

I found mine, a lot of 5, in a box of miscellaneous junk in the floor at Young's Engineering in Salem MA in about 1975.  I think they charged me less than $10 for all of them.  One tube had an intermittent filament-grid short, I just recently dropped one and ruined the filament, but still use the others.  Since then I have acquired another NOS pair as a spare.  They are also good, but don't seem to quite have the modulation linearity that my originals have.

The plate appears to be made of the same material as that of 833A's.  As with the latter, it is very easy to overheat the plate and burn in a shiney spot, but that doesn't seem to affect the operation of the tube in the slightest.

One of out pubes looks like a mirror on one side of the plate. It is in use today so guess the thing is going to hang in.