McIntosh MC-30 A-116-B Mono Tube Amplifier MC30, TESTED WORKING, CLEAN low S/N
McIntosh MC-30 A-116-B 모노 진공관 앰프 MC30, 작동 테스트 완료, 깨끗한 낮은 시리얼 번호
| 상품번호 | 206338373294 |
| 상태 | Used |
| 거래유형 | 즉시구매 |
| 출고국 | 미국 (US) |
이베이 판매가
$2,125
약 3,132,250원
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상품 설명
This is from the estate of a friend that passed away. When I found it, it was under a handmade fabric dustcover in a cardboard box. It appears to have been there long enough for the AC power cord to lose its flexibility. When I tried to straighten the line cord, small chunks of insulation fell out of it. So I cut the line cord off, both to prevent someone from plugging in an unsafe cord and to avoid having little pieces of insulation spread around the house while I evaluated and photographed it. I had initially planned to sell this unit untested, but later decided to replace the AC cord and test it. So some photos were taken before I replaced the AC cord, and some after. According to the McIntosh Compendium, MC 30 - Sold from July 1954-June 1962. S/N: 10,000~23,655 & 1E001~10E592 (14,246 UNITS). With serial # 10865, (the 865th unit made) it probably dates to late 1954 or early 1955.
When I removed the bottom mounting plate to look at the condition, I was amazed. I used to do repairs of audio gear like Fender Bandmaster amps and I have never seen a chassis that looked like it just came off the production line. (That dust cover must have been in place the vast majority of this unit's life)! The components all look like 1950's vintage. The chrome chassis and tube ID stencils are still in great condition (see photos). There are a few scuffs on transformer covers.
Other observations: There is no evidence of the chassis ever having had a McIntosh dimensional logo on either the front or rear panels (there are labels instead). It seems the early units didn't have logos. The power tubes are metal envelope RCA 1614 tubes (a ruggedized 6L6). From the outer envelope appearances, one of the tubes appears to have seen more heat than the other one. I tested the two 1614 power tubes and the 5U4 tube and they all tested good.
To save you some time, if you plan to put newer capacitors in this unit, it is early enough that it uses a Sarkes Tarzian 026-28H-Q selenium rectifier for the negative bias circuit. Later schematics for revised versions of this amp use a silicon diode rated 400 PIV 10mA. Do a search for "McIntosh - MC30 Service Manual & Schematics" for good (but not printable) information about this unit.
After I replaced the AC cord, I checked a few voltages as a sanity check, then connected a big 10 ohm load resistor with an attenuated speaker (I don't have a big 8 ohm), scope, and multimeter to the 8 ohm output and connected an oscillator to the input. I eased up the line voltage with a Variac to give the electrolytic capacitors a chance to reform after decades without any applied voltage. I don't have the equipment to do proper tests to confirm the unit is or isn't within specs, but I tested how it performs at several frequencies. With 1 kHz input, I adjusted the oscillator amplitude up until I could hear the onset of distortion and recorded the scope trace and meter reading. I repeated the procedure at 20 kHz (where my multimeter is no help since it has an AC frequency response of 1 KHz). Then I did the same test at 60 Hz and 20 Hz. The amp specifications say the output should be within .1 dB @ 20 Hz 30W. The amp is expected to deliver 15.5 VAC from the 8 ohm output terminal into an 8 ohm load. I tested with a 10 ohm load on the 8 ohm output, so the power delivered to a 10 ohm load is expected to be less than with an 8 ohm load. The maximum power at 60 Hz could be within specs, but at 20 Hz the output is lower than specifications (I measured 11.97 VAC into a 10 ohm load, voltage output would be less into an 8 ohm load). I would guess that some capacitors (high voltage electrolytics or coupling caps) have lost some capacitance. The low end response droop at 20 Hz would not be a problem for me since I can't hear anything at 20 Hz (or 20 KHz), but it might matter to someone with better hearing than mine.
I will ship the unit double boxed.