1965 Vox AC100 Head - Model Used By the Beatles, Stones, Who, etc. - Restored

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

1965 Vox AC100 Head - Model Used By the Beatles, Stones, Who, etc. - Restored :
$3300.00

In order to avoid possible shipping damage, I very much preferfor the buyer to pick up this amp or making arrangementsto meet. I am willing to travel a reasonable distance.

This amp has been fully gone through and serviced.l will let the photos above and my tech\'s notes aboutthe work he did on this amp with his observations which are in blue below describe this amp (my own comments appear in red):

1.Stripped down and cleaned chassis, removed rust and remaining original zinc chromate plating. Straightened and reformed damaged areas at bottom of chassis near captive nut areas.

2. Recoated with two coats of clear acrylic lacquer.

3. Replaced defective screen resistor (5W 100 ohms)

4. Replaced burned and poorly dressed internal wiring as needed.

5. Replaced Fender Dual Showman output transformer with Mercury Magnetics “Tone Clone” type. Tested Fender transformer in circuit. It worked as well as the Mercury.

6. Repaired Woden vertical choke wiring and rewrapped windings. Date code on choke is FW which indicates June of 1965.

7. Straightened and remounted face plate.

8. Checked all tubes. One 6CA7 required pins resoldered. Installed 12AU7A in V1 position, 12AX7A in V2 and V3 positions.

9. Checked all electrolytic capacitors O.K.

10. Installed a new input jack at “A” position.

11. Installed 10-32 captive nuts on chassis (6) positions.

12. Removed worn and broken case chassis rails. Straightened bent lower vent screens.

13. Made up replacement case chassis rails, installed and painted light coat of flat black. The original chassis rails are included. My tech said they looked like scrap wood!

14. Installed 10-32 Tee-nuts in case (6) positions. Rear panel screws are 1\" stainless steeloval slotted with stainless steel finish washers.

15. Routed out damaged rear panel wood. Made up hardwood plugs for routed holes and glued into place. Bored new clearance holes in plugs and painted plugs. The inside of the rear panel where the holes are for the speaker and power receptacles looked like they had been gouged out with a drill. See last photo for this repair.

16. Installed Switchcraft speaker (3 pin) and power input (4 pin) receptacles to back panel.

17. Wired speaker and power receptacles. (Speaker wiring is pin 3 positive, 1 and 2 negative.) Amp is set to 8 ohm load now. Power is safety ground to shell and pin 1, L1 (hot) to pin 2, pin 3 has no connection and pin 4 is N (neutral).

18. Made up 8’ power cord to above specifications.

19. Made up 6’ speaker cord to above specifications.

Observations on this amplifier.

It has been repaired a few times. A 3.5 volt Zenner diode has been added to the Zenner bias string to raise the output tube bias a bit. This is a good thing; I did this on the earlier VOX100/2 you gave me using a slightly different technique. Output tubes have shorted out before since all the screen dropping resistors have been replaced. The voltage select switch is inoperative but in the US, it is not needed. The schematic shows V3 with pin 2 as the input and pin 7 the response but in both amps I have seen, the situation is reversed. The bias generation coupling capacitor C15 failed on both units and has been replaced with series capacitors of twice the nominal value in series for better performance under the high voltage that destroyed the factory originals. Both amps have a zero signal power consumption of about 1.5 amperes @ 120VAC input and about 3 amperes at full power output (clipping into 8 ohm load).

The schematic shows a 3 ampere fuse in the power line. The 4th edition of the Radiotron Designer’s Handbook states that during power up of transformer coupled power supplies, currents of up to 20 times rated input current may be developed for less than 0.01 seconds. (Page 1281). They recommend slo-blow fuses. A test of this amplifier was made using a calibrated AC ammeter and switching the amplifier on and off for twenty trials at random times while monitoring the input current. Transients of up to 10 amperes were seen on two of the twenty trials and transients of 5 amperes were seen on 6 other of the twenty trials. These transients will cause a 3 ampere slo-blow fuse to fail, especially if it has just seen service under power or sees a power glitch while under power. I installed a 5 ampere slo-blow fuse and no further problems were seen with blowing fuses. The 3 ampere rating likely reflects service at 220VAC as would be the case in England. In that case, 3 amperes would be sufficient to handle surges. There is no specification on the schematic as to the mains input voltage.

The amplifier is a noisy beast. It has 100mv of hum signal into 8 ohms. This is due to the minimal filtering done at the output. In fact the output transformer center tap has no direct connection to a filter capacitor. For reference, the center tap ripple is 75 Volts P-P, the choke input ripple is 10V P-P and the choke output ripple is 80 mv. P-P. The AC100/2 I worked on before had been modified by a repair shop to have filter capacitors on the output center tap and added more at the choke input. It was a quieter amplifier for having the capacitors added but it was not original. I did not take ripple measurements on this amplifier. The hum the original makes becomes totally inaudible as soon as the musician begins to play so musically it does not matter and it does sound exactly as the live recordings of the late 1960’s and early 1970’s did during breaks in the music. The tone control section of this unit has a modest treble control and a bass control that provides bass cut in the CW direction, definitely unusual but as provided by the factory. Plate supply is 475 VDC and the output tubes draw about 30 ua. control grid current each; at about -29 volts bias. Power output is the same for either 8 or 16 ohms at about 56 WRMS.

The amp is in fine condition now. It has a wonderful tone and huge power and is the lightest and smallest 100 watt tube head I know of.