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Help Needed With MAC 1500 Receiver Matter

A

Avogadro33

Member
Help Sought From the McIntosh Collector Gurus

I have both MAC 1900 and MAC 1700 receivers in my collection. Both take the McIntosh L-19 wood cabinet, which I have for each (though it is a bit deeper that really needs to be for the 1700).

I also have a Mint/Near Mint MAC 1500 in my collection. (Yes, extremely rare in any condition.) I’ve been looking for a McIntosh wood cabinet for the MAC 1500 for a long time. After that long search I recently located a McIntosh L-19 wood cabinet that had been used on a MAC 1900. Well, the L-19 wood cabinet that had been on the MAC 1900 does NOT FIT onto the MAC 1500! The width is fine; the problem is the interior height. The output tubes’ height it a bit too much for the interior height of the L-19 cabinet. The cabinet interior height needs another one-quarter inch. I’ve seen a photos of a MAC 1500 receiver with a wood cabinet. Can someone tell me what’s going on?
_ _ _ _ _ _

Follow-Up, as IT JUST OCCURRED TO ME:

Perhaps the problem might be the particular 7591 output tubes in the receiver (which may or may not be the originals). The tubes currently in the receiver are 3-1/4 inches high (from the bottom of the plastic base to the top of the tube). They read as follows:

7591AEH
electro-harmonix
Made in Russia
13 05

Is there another brand of 7591 tube (that will be appropriate for the MAC 1500) that is a bit shorter ---- maybe a quarter-inch less tall?

Thank you.
 
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WOW! Never even heard of the L-15WO cabinet.

As I amended my original post, I thought I might have had after-market 7591 output tubes that were a bit too tall. Since your moniker is "VintageMac/McIntosh Junkie", I guess you know.

So, while it took a lot of effort to find the L-19 cabinet (which I had read would fit the MAC 1500), I now understand that it's going to be a lot harder to find an "L-15WO" cabinet! All the receivers in my collection have wood cabinets. Anyone want to purchase my MINT/NEAR MINT MAC 1500 receiver without wood cabinet?!!
 
Howard, the button base GE 7591A tubes might be a better fit at 2.690 inches from the bottom of the base to the top of the glass. Be prepared to spend some money for them though.
Doug
 
Doug, thank you.

I have little knowledge of tubes. I noodled around the Internet for GE 7591A. I did not find any that were described as 2.69 inches tall. Can you suggest where I should look?

Also, if I buy these and they fit (see my original post), should I have the MAC 1500 receiver re-biased?

Thank you for your help.

Howard
 
Modern Tung Sol 7591 are reported to fit on mac1500/ma230 within a mac cabinet. Should fitwithin your cabinet.
 
This problem has been reported with the EH 7591A tube and some Fisher products as well -- the output tubes are too tall. Use of the reissue Tung Sol 7591A reportedly solves that problem with Fisher gear, and might very well with your Mac unit as well.

Dave
 
Correct- the EH 7591 tubes will not fit the L19WVO cabinet nor will they fit the cabinet for a Fisher receiver either. Order a set of Tung Sol 7591 which are the same size as the OEM Sylvania/Westinghouse 7591.
 
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Avogadro33 said:
Doug, thank you.

I have little knowledge of tubes. I noodled around the Internet for GE 7591A. I did not find any that were described as 2.69 inches tall. Can you suggest where I should look?

Also, if I buy these and they fit (see my original post), should I have the MAC 1500 receiver re-biased?

Thank you for your help.

Howard
Click to expand...
You must re-bias when any or all of the output tubes are replaced.
 
When Terry DeWick restored my MAC1500, he provided the following advice:

1. Bias
- Bias should be .5 to .7 Volts at test points next to tubes.
- Pots are under panel.


2. Replacement tubes:
- Electroharmonics (EHS) (too tall for case)
- JJ Tesla (will fit inside case)
 
Heard not so good things about JJ. With a brand new set of four JJ 7591, one would flare up brightly on initial startup before returning to normal glow and have also heard they fail in a "spectacular" way possibly resulting in damage to the unit. While they do fit the cabinet, the Tung Sol seem to be the better choice and price difference is small.
 
62caddy said:
Heard not so good things about JJ. With a brand new set of four JJ 7591, one would flare up brightly on initial startup before returning to normal glow and have also heard they fail in a "spectacular" way possibly resulting in damage to the unit. While they do fit the cabinet, the Tung Sol seem to be the better choice and price difference is small.
Click to expand...

Added this to my notes. Thanks!
 
Second on staying away from JJ's. I have a set of EH7591's in my Scott 340B and they work well but I don't use a case and the sockets have plenty of room around them.
 
My EH do emit a blue glow. The blue glow was more present in my MA230 than in my MC225. It is very pleasant to look at--more pleasant to me than blue meters.
 
I’ve heard it said that blue glow from tubes is an indicator of becoming weak and ready to fail. I know this was the case with the Sylvanias in the receiver when I got it. Apparently not always. The Tung Sols burn the typical amber color.
 
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I always understood a blue glow to be gas/contamination in the envelope, I don’t recall where that information came from.
 
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