Tube rolling in my recently acquired MAC 1700 with the original tubes...

Dr. Ears

Super Member
First, I replaced the two Nuvistors with NOS ones from the 1930's to 1940's and immediately noticed more bass.
Next, I replaced the gray plated 6AU6 with an RCA black plated one, then I replaced the Telefunken 12AU7 with a black plated RCA 5814 from the 1950's, which gives you more detail, but I am not certain that I prefer the RCA 5814 over the Tele 12AU7.
Incoming are a smooth plated Tele 12AU7, black plated 6HS6's, a Mullard 6EA8, a black plated 6CS6 and a Telefunken 6AU6.
Fortunately none of the tubes are very expensive.
I will report back after I have heard it's new tube compliment.
 
Nuvistors were amongst the last "new" tube types, introduced fairly late in the 1950s. They are generally used in the FM tuner front end and shouldn't affect sound in that position, tho, randomly replacing tubes in the tuner section can and will affect performance thru altering IF / mmltiplex alignment.
 
Nuvistors were amongst the last "new" tube types, introduced fairly late in the 1950s. They are generally used in the FM tuner front end and shouldn't affect sound in that position, tho, randomly replacing tubes in the tuner section can and will affect performance thru altering IF / mmltiplex alignment.
That is why I am rolling tubes prior to getting it professionally serviced, but the date codes on the Nuvistors clearly indicate that they were made back in the late 1930's.
 
That is why I am rolling tubes prior to getting it professionally serviced, but the date codes on the Nuvistors clearly indicate that they were made back in the late 1930's.
Wrong numbers then, not date codes. If they were acorn tubes I could go with that. RCA intro'ed the Nuvistors in their New Vista Color sets around 1959/1960.
 
Wrong numbers then, not date codes. If they were acorn tubes I could go with that. RCA intro'ed the Nuvistors in their New Vista Color sets around 1959/1960.
Thank you very much, the print is so small that I could have easily read it wrong.
When testing these I had to test 10 to find 4 that tested at the max on the tester I was using.
Oddly, they were either dead or maxed out the needle.
 
Nuvistors were amongst the last "new" tube types, introduced fairly late in the 1950s. They are generally used in the FM tuner front end and shouldn't affect sound in that position, tho, randomly replacing tubes in the tuner section can and will affect performance thru altering IF / mmltiplex alignment.
I took your advice and used the exact same tubes that Mcintosh spec'd.
Fisher & Mcintosh owners only use legitimate 6HS6's, which were a very limited production tube and there is NO exact replacement for them.
Beware of mislabeled tubes, the real ones were only made by RCA & Sylvania, look carefully for 6HS6 etched in the glass, not what is printed on the glass.
 
My Scott 340B takes one 6HS6, at the time I got mine the 6HS6 was beginning to get expensive but not by whole lot. I got a dud then certain I got the real things, now I have two spares. The original still works fine. Luckily my Fisher 400 is the version that doesn't use one.
 
My Scott 340B takes one 6HS6, at the time I got mine the 6HS6 was beginning to get expensive but not by whole lot. I got a dud then certain I got the real things, now I have two spares. The original still works fine. Luckily my Fisher 400 is the version that doesn't use one.
I am wondering if the Mcintosh repair / restore places keep a stock of NOS tubes?
The MAC 3500 & 3500 II feature nothing short of amazing technology, but it requires eight 6LQ6's in the critical output stage.
If, you are lucky enough to afford MAC equipment how do you acquire the tubes that are no longer in production for them?
It took me 3 weeks to find and buy NOS tubes for my MAC 1700.
I mentioned the 6HS6 because of it's limited production, my long time dealer and friend, stocks 3 million tubes and only had six of them.
I have been rolling tubes for over 40 years and own six tube testers, none of which are working the way I would like them to, but having owned them and others gives me an edge, when pursuing tubes on Epay.
Yesterday, I won an auction for a smooth plated Telefunken for $9.99, which by the seller's tube tester read NOS.
I was able to win this auction probably because I was familiar with how B & K tube testers read, which is very different from the Hickok's, which most people are familiar with. In this case, the tester read 90 / 95, minimum good is 65 and the needle only goes up to 100.
Don't buy a tube tester unless you are in the business of selling vacuum tubes, there are enough honest dealers out there, who keep their testers in good working condition. If, you have to pay to have tubes tested, it's worth it and beats trying to keep a tube tester in working condition.
 
Just for the record, the tubes in a MAC1700 are used for the tuner section only.

Tube selection will have no bearing on SQ of other sources played through the unit.
 
Just for the record, the tubes in a MAC1700 are used for the tuner section only.

Tube selection will have no bearing on SQ of other sources played through the unit.
I know and I think the tuner should go on either when the tuner is selected or buy it's own on / off switch.
This way we are burning the tubes like light bulbs, when the tuner is not selected.
 
I don't know what are you pursuing, If the unit is working properly tubes there will last for a very long time, rolling tubes there can put the the tuner out of alignment, and do not affect sound.
It is a solid state device.
 
I know and I think the tuner should go on either when the tuner is selected or buy it's own on / off switch.
This way we are burning the tubes like light bulbs, when the tuner is not selected.

Ideally yes but presumably that would require extra circuitry (or independent power supplies) to prevent the other sections of the unit from receiving more voltage when the tubes are shut down. Terry specifically advises against the removal of "unused" tubes for this reason. In any case, the signal type tubes used in the tuner section have extremely long lifespans.

Even at 50+ years of age, both my MAC1500 & MX110Z still sport their original tuner tube compliment while still meeting factory spec- the only exception being the 6D10 Compactron in the MX110 that was only replaced two years ago.
 
When I got my MAC1700 I did a complete tube swap. Only one of the tubes was actually bad but I swapped all of them anyway for good measure. Resulted in a solid performing tuner that will last for years and a nice cache of old tubes I've used in various devices over the years. Especially the Telefunkens ;)
 
When I got my MAC1700 I did a complete tube swap. Only one of the tubes was actually bad but I swapped all of them anyway for good measure. Resulted in a solid performing tuner that will last for years and a nice cache of old tubes I've used in various devices over the years. Especially the Telefunkens ;)
I just completed the same complete tube swap, which I wanted to do prior to having the unit serviced and partially restored.
With some of these tubes, it's buy them when you can, not when you have to!
This is my new tube compliment:
New Nuvistors, 6DS4's, which are identical to 6CW4's, no choice here RCA made all of them. A fresh pair of 6HS6's, little choice here I went with RCA's over Sylvania's, these tubes are getting scary rare and there is no exact substitute. NOS Telefunken's in the 6AU6, 6CS6 and ECC82 holes, this tuner loves Telefunken's. I rare NOS TungSol black plate in the 6EA8 hole, I also have Mullard & GE 6EA8's.
Inbound are a rare NOS pair of Siemen's ECC82 with silver (nickel) plates. I expect the Siemen and Tele to shoot it out fir the 12AU7 spot, if my past experience holds true, the Siemen will be more detailed and the Tele smoother with a somewhat bloated mid-range.
 
Swapping tubes in the tuner section will most likely do more harm to the alighnment than good......you might get lucky and get a better alighnment if you swap out a funky tube but.....it is iffy.

You have also remember that the original owners expected the tuner to be instantly available when switching from their turntable or tape machine......they did not want to wait for the tuner to warm up, start receiving and eventually sound good while the were switching sources.

Being the "age of tubes" they also were conditioned to service expectations whether their tube TVs or stereos. People didn't throw away their cars or electronics they had them serviced.

Besides every corner drugstore had a tube tester and cabinet of RF tubes.
 
All my tuners and receivers, including an MX 110 and MR 67 still have most of the original tuner tubes. I can only be certain on my two Macs that the only tubes I’ve changed have been the 6U8’s in the MPX sections and a 6BL8 in my Scott 340B’s MPX section. There is a tube or two not labelled McIntosh in my 67 and 110, I know at least one of them is RCA. I received the units that way. My Fisher 400 has all the original tuner tubes. They definitely tend to be long lived.
 
All my tuners and receivers, including an MX 110 and MR 67 still have most of the original tuner tubes. I can only be certain on my two Macs that the only tubes I’ve changed have been the 6U8’s in the MPX sections and a 6BL8 in my Scott 340B’s MPX section. There is a tube or two not labelled McIntosh in my 67 and 110, I know at least one of them is RCA. I received the units that way. My Fisher 400 has all the original tuner tubes. They definitely tend to be long lived.
I saved all the original tubes and bought exact replacements in all cases. I wanted a fresh set prior to having my unit serviced.
As of now, I would say the tuner is cleaner sounding and it got me back into listening to FM at home.
 
I saved all the original tubes and bought exact replacements in all cases. I wanted a fresh set prior to having my unit serviced.
As of now, I would say the tuner is cleaner sounding and it got me back into listening to FM at home.

My re-tubing of my MAC 1700 is now complete, I wanted a fresh set of tubes, prior to having it serviced and the tuner re-aligned.
Four out of the eight tubes offer you little choice, the Nuvistors 6DS4 / 6CW4 are identical and they were only made by RCA.
The pair of 6HS6's were only made by RCA & Sylvania, I went with NOS RCA's, be careful with these, despite what you read there is no exact replacement for these scarce tubes.
I replaced the gray plated GE 6EA8 with a rare black plated TungSol 6EA8.
The other three tubes, the 6AU6, the 6CS6, and the 12AU7 with long smooth plates are all Telefunken's, which are normally not my go to tubes, but this tuner just loves Telefunken's and I expect this set of tubes to out live me.
 
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