Maintenance. If you are a hands-on audiophile like many of us, you occasionally face the task of updating\/repairing your system\u2019s components and ancillary devices. I personally love vintage tube audio gear, which has its own set of maintenance chores: checking the tubes periodically with a tube tester, cleaning the tube pins, replacing power supply capacitors, or the notoriously problematic (after 50 years of use) bumblebee capacitors such units may contain. <\/p>\n\n\n\n
For many lovers of vintage tube audio gear, the holy grail of preamplifiers is, perhaps, the Marantz 7 and\/or the McIntosh C-22. These two items from the late 1950\u2019s through late 1960\u2019s have become quite scarce and, as a result, have risen dramatically in price on the popular auction sites. I was incredibly lucky back in 1993 to acquire a Marantz 7 via a trade of audio gear with a gentleman near the Blue Ridge Mountains. He had inherited this pristine piece of gear from his uncle many years prior. However, he became tired of periodic tube replacement and occasional trips to the repair shop for slight issues beyond his own capabilities. I was thrilled to acquire this piece of hifi history and, having already built a few kits (Heathkit, Dynakit), felt ready to take on a revered component for the long haul. <\/p>\n\n\n\n
The immediate needs for this preamplifier immediately after my acquisition were new caps on the top mounted phenolic board. One \u201cbumblebee\u201d capacitor (named for their black body, surrounded by colored stripes) had a big crack running from one end to the other. While many aficionados consider it heresy to replace any of the active components in a vintage (and valuable) piece of collectible audio gear, I now had my excuse to update this preamplifier with some newer, better performing modern components. I replaced all of the capacitors on the top phenolic \u201cturret\u201d board with boutique-type TRT SETI Infinicaps, a couple Hovland MusiCaps, and fresh Nichicon Muse and Sprague Atom small electrolytics. I replaced the tubes, six 12AX7A\u2019s, as well. With periodic tube replacement, this preamp has now served my \u201cupstairs system\u201d exceptionally well for nearly thirty years. However, as you may have guessed, now I\u2019m going to relate my most recent maintenance on this revered piece of gear\u2026<\/p>\n\n\n\n
I have mentioned the top facing phenolic\/turret board in the Marantz 7. It is not a circuit board, the components are hard wired to \u201cturret-type\u201d posts, not traces. <\/p>\n\n\n\n<\/figure>\n\n\n\n<\/figure>\n\n\n\n
This board is also attached to a metal flange that contains the horizontally mounted 12AX7A tube sockets, which protrude from the back panel. To reduce the deleterious effects of vibration (creating undesirable microphonics), this board and metal flange \u201cfloat\u201d on three metal\/rubber suspension screw-in \u201cgrommets\u201d. <\/p>\n\n\n\nTwo \u201cnew\u201d suspension mounts next to a \u201cbad\/broken\u201d mount<\/figcaption><\/figure>\n\n\n\n
These are crucial to the design of the preamp, and mine had (as is common) deteriorated to the point of splitting in the middle of the rubber and separating. Instead of floating, the board was resting, undesirably, on the chassis. <\/p>\n\n\n\n
Fortunately, an enterprising audiophile\/businessman in Hong Kong had acquired a stock of NOS (new old stock) metal-rubber isolation\/suspension mounts years ago and kept them in an oil bath, keeping them fresh. I was lucky enough to acquire a set about five years ago and had been waiting for the perfect moment to install them ever since! <\/p>\n\n\n\n
This week, I got into the proper mood to finally undertake the task of installing them. The job was not nearly as difficult as I had feared. In fact, it took me longer to remove all the interconnects and tubes and disassemble the unit than it took to complete the task. Now completed, the turret board and tubes float on the suspension mounts as they are supposed to! <\/p>\n\n\n\n
While I had the unit open, I took the time to also spray the insides of the balance and volume controls with Deoxit FaderF-5 to lubricate and clean the wipers in these controls, which should eliminate any scratchy issues with either pot. I also used the same solution to clean the contacts on the selector switch. Another nice tweak I like to do is clean all the tube pins with an emory board. This removes any oxidation or possible corrosion on the pins ensuring better contact. If you decide to replicate this tweak, however, make sure to do this gently\u2014you don\u2019t want to thin the pins, which could result in looser tube pin tension. <\/p>\n\n\n\n
Lastly, I checked the tubes on my trustworthy Hickok 800A tube tester. Tube testers are essential if you want to eliminate that nagging, paranoid feeling when you suspect, but don\u2019t definitively know if your tubes are nearing the end of their useful life. In my opinion, too many audiophiles replace tubes before they really need to. My GE 12AX7A\u2019s in the Marantz 7 have served faithfully for over five years and they still tested strong! While quality tube testers have become pricey on the used market the past ten years or so, I am a firm believer that if you are going to utilize tube components in your system, you must own or have access to a quality tube tester. <\/p>\n\n\n\n
When buying a tube tester, make sure it\u2019s a mutual transconductance-type tube tester, not an emissions tester. Two of the more common and best performing mutual transconductance-type tube tester brands are Hickok and B&K. The Hickok 539C is the holy grail of Hickok tube testers but the 800A, 600A, 6000, 533A, 752 and others are all great testers. I also like the B&K 700 and 707 testers. If you don\u2019t want to pay the high price found on the popular auction sites, go to a local AARL sanctioned Hamfest. Now that things are opening back up a bit\u2026you might find a bargain! Realize, however, that testers should be calibrated and the (usually two) rectifier tubes inside them must be good or replaced. <\/p>\n\n\n\n
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