VTA Mark 1 Owners manual

1

Contents

Introduction ……………………………………………………………………………. 2

Front Panel …………………………………………………………………………….. 4

Rear Panel ……………………………………………………………………………... 5

Installation ……………………………………………………………………………… 6

Bias Adjustment ………………………………………………………………………. 7

U/L and Tetrode Mode ……………………………………………………………….. 8

Tube Replacement ……………………………………………………………………. 9

Fuse Replacement ……………………………………………………………………. 12

Maintenance …………………………………………………………………………… 13

Troubleshooting ………………………………………………………………………. 14

Specifications …………………………………………………………………………. 15

Maintenance Log ……………………………………………………………………… 16

Warranty ………………………………………………………………………………… 17

2

Introduction

THANK YOU for purchasing the VacuumTubeAmps.com Mark 1 Power Amplifier, designed,
engineered and hand built in the U.S.

Features:

User selectable Tetrode or Ultra Linear modes via a front panel switch.

Front panel bias controls for each of the four 7591A output tubes allows the audiophile to
balance the output stage for perfect push-pull operation.

Four high quality analog front panel meters allows for continuous monitoring of the output
stage, and provides an early warning of possible tube failure.

Gold plated RCA input sockets.

Gold plated five way speaker jacks.

Gold plated tube sockets

Soft start power supply greatly extends the life of components and tubes.

High end potted output transformers provides a choice of 4Ω or 8Ω speakers.

Toroid power transformers are used for high efficiency and low magnetic radiation.

Thermostatically controlled ball bearing fan exhausts heat for long life.

Variable density isolation feet.

Beautiful solid oak side panels for a power amplifier that looks as great as it sounds.

Thank you again, and enjoy your new Mark 1 Power Amplifier!

Michael A. Burrows, Owner, VacuumTubeAmps.com.

Email: [e-mail]

Fax: [phone]

All rights reserved. No part of this publication may be reproduced, or transmitted, in any form or by any means,
electronic, mechanical, recording, or otherwise, without the prior permission of VACUUMTUBEAMPS.COM.

3

Front Panel

1 POWER SWITCH Turns power on or off. The Mark 1 incorporates a time

delay circuit that delays startup to allow the tubes to warm up before high

voltage is applied to the various amplifier stages.

2 U/L – TETRODE SWITCH

3A-6A BIAS METERS Provides a visual indication of the four output tubes.

3B-6B BIAS CONTROLS

on the four output tubes.

User accessible controls for adjusting the bias voltage

Provides a choice between U/L and Tetrode mode.

4

Rear Panel

1 Input Jacks

a red band; left channel jack has a white band.

RCA jacks for connection to a line amplifier. Right channel jack has

2 Ground Screw For connecting to ancillary equipment.

3 Left Speaker 5 way binding post.

4 Right Speaker 5 way binding post.

5 Speaker Impedance Switch Allows matching for 4Ω or 8Ω speakers.

6 Cooling Fan Cools the MARK 1.

7 AC Power Connector/Fuse For connection to a 120VAC receptacle, and

5 X 20 MM fuse.

5

Installation

1. Carefully unpack the shipping box and save for future use. Don’t touch the front panel bias
controls.

2. Set the MARK 1 in a place that is out of reach of children and pets, and away from sources
of moisture and water.

Caution! Do not put the Mark 1 in an enclosed cabinet! This power amplifier

produces heat, and must have at least three inches of free space between the fan and
wall, and at least twelve inches of free space above the top of the unit. Do not set the
unit on any material (carpet, foam, etc.) that can block the ventilation holes on the
bottom of the unit.

Warning! Never place anything on top of the Mark 1! To do so increases the risk of

fire, and will greatly reduce the life of the unit.

3. Do not connect your preamplifier or line stage at this time.

4. Set the Speaker Impedance Switch to match your speakers impedance.

5. Connect your speakers to the Left/Right Speaker binding posts. The black post connects
to the negative (-) speaker wire. The red post connects to the positive (+) speaker wire. Do
not use a wrench to tighten the binding post, otherwise they might break.

6. Never operate the Mark 1 without a speaker connected! Always turn off the unit before
connecting or disconnecting speakers.

7. Make sure the Mark 1’s power switch is off.

8. Insert the AC power cord connector firmly into the AC/Fuse socket on the back of the unit
below the fan. Insert the other end into a 120VAC, 60Hz receptacle.

9. Set Bias controls, next page.

6

Bias Adjustment

The MARK 1 has four user adjustable front panel bias controls, as well as four analog meters
for monitoring the output tubes.

The meters were properly adjusted before shipping. However, the meter’s pointer may have
shifted slightly during shipment.

Using a small flat-bladed screwdriver, slowly turn the pointer adjust screw (located just below
the meters’ bezel) so that the pointer is exactly on the “0” tick mark.

With only the speakers connected, turn on the MARK 1. After about thirty seconds, the
meter’s pointer will briefly swing to the right. Initially adjust each bias control so that the
pointer indicates 24 mA (milliamperes). Each major tick point represents 10 mA, while each
minor tick point represents 2 mA.

Keep the MARK 1 turned on, and watch the meter’s pointers slowly move to the right as the
unit warms up. Make sure that the pointer does not go above 30 mA as shown in the
illustration.

After two hours, adjust the bias controls so that all meters read 30 mA.