The Trinity Tweed Amp Builder's Guide USAGE STRICTLY RESERVED FOR TRINITY AMPS CUSTOMERS ONLY DO NOT DISTRIBUTE Version 3.2 Parts © Trinity Amps 2005 - 2018 www.trinityamps.com Version 3.2 Page: 2 Table of Contents Introduction .......................................................................................................................................... 5 Acknowledgements .............................................................................................................................. 5 WARNING .......................................................................................................................................... 6 Please Read this Information Carefully ............................................................. 6 Version Control .................................................................................................................................... 7 Guitar Amplifier Basics ....................................................................................................................... 8 Fender and Marshall tone controls .............................................................................. 9 Interactive Volume Controls – Fender Tweed Amps .................................................. 12 Distortion .............................................................................................................. 14 Introduction to Vacuum Tubes and Common Terms ................................................................. 17 Input Jack Theory .............................................................................................................................. 20 Circuit Description ............................................................................................................................. 21 Original Circuit with outlined stagesTweed Specifications .......................................................... 22 Fender amps own the blues … ........................................................................................................ 24 Building an Amp ................................................................................................................................ 26 Introduction ........................................................................................................... 26 Switches and wire ................................................................................................... 26 Physical layout ........................................................................................................ 26 Grounding ............................................................................................................. 26 Insulated jacks ........................................................................................................ 27 Minimizing transformer interference ......................................................................... 27 Wiring ................................................................................................................... 27 Assembling the amp .......................................................................................................................... 27 Before You Begin ................................................................................................... 27 Tools ..................................................................................................................... 27 Soldering................................................................................................................ 28 Tube Pin Numbering .............................................................................................. 28 Assembly Steps Summary ........................................................................................ 29 Mounting Hardware Locations ................................................................................. 30 Install Hardware ................................................................................................................................. 30 Wiring ................................................................................................................... 32 Install Power Transformer ................................................................................................................ 34 Wiring the Tweed Rectifier Socket ................................................................ 35 Trinity Tweed Grounding Scheme ................................................................. 35 Mains Power Connection ............................................................................ 36 Testing the Power Transformer ................................................................................ 40 Install the Output Transformer - Output Jacks .......................................................... 40 Impedance Switch ................................................................................................... 41 Assemble the Eyelet Board ............................................................................................................... 43 Connecting the Board ................................................................................ 45 Connect Board to Potentiometers ................................................................. 45 Input Jacks .......................................................................................................................................... 47 Final checkout..................................................................................................................................... 48 Working Inside A Tube Amplifier Safely ................................................................... 50 Unplug ................................................................................................... 50 Sit .......................................................................................................... 50 Version 3.2 Page: 3 Drain ..................................................................................................... 50 Test ....................................................................................................... 50 Close ...................................................................................................... 50 Making a Voltage Measurement ................................................................................ 51 Discharging the Power Supply.................................................................................. 51 General Amplifier Operation ........................................................................................................... 53 Some DO NOTS .................................................................................................... 53 Trinity Tweed Voltage Chart ............................................................................................................ 54 WARNING ........................................................................................................................................ 55 Please Read this Information Carefully ........................................................... 55 Troubleshooting ................................................................................................................................. 56 Hum ...................................................................................................................... 56 Volume Test .......................................................................................................... 56 Faulty tube ............................................................................................................. 56 Severely unmatched output tubes in a push pull amplifier ........................................... 56 Faulty power supply filter caps ................................................................................. 57 Faulty bias supply in fixed bias amplifiers .................................................................. 57 Unbalanced or not-ground-referenced filament winding ............................................. 57 Defective input jack ................................................................................................ 58 Poor AC grounding................................................................................................. 58 Induced hum .......................................................................................................... 58 Poor internal wire routing ........................................................................................ 58 Poor AC Chassis Ground at Power Transformer ....................................................... 58 Defective internal grounding .................................................................................... 59 Hiss ....................................................................................................................... 59 Metal Film Resistor Substitutions ............................................................................. 59 Squealing/Feedback ................................................................................................ 59 Radio Interference .................................................................................................. 60 Scratchy Sounds on Potentiometer(s) ........................................................................ 60 Amp Buzz or Rattle When Installed in Cabinet .......................................................... 60 Tone Tweaking ................................................................................................................................... 62 More Tips for fine tuning your amp .......................................................................... 63 Running 6L6 Output Tubes ............................................................................................................. 64 Tube Substitutions ............................................................................................................................. 67 How to read Resistor Color Codes ................................................................................................. 68 How to read Capacitor Codes .......................................................................................................... 69 FAQ ..................................................................................................................................................... 71 TWEED Bill of Materials (BOM) ................................................................................................... 73 Trinity Amps Schematics and Layouts ............................................................................................ 74 Version 3.2 Page: 4 Introduction This guide has been prepared for builders of Trinity Amps Kits. It is always being improved and we would appreciate your feedback and comments to: [email protected] Accordingly, content and specifications are subject to change without notice. We do try to make it as accurate as possible, but it is sometimes hard to keep up with the changes. Therefore, if you do find an error, please let us know about it and we will correct it. Suggestions are welcome so if you have one, please get in touch with us. Sources of help. Forums: Please use the various forums to get help. They are an excellent resource and can be found at trinityamps.com Fender forum. The Fender Amp Field Guide is a terrific resource for all amps Fender Email: We can’t help with every problem but if you can not get your problem resolved, email us and we’ll do our best to help. Phone Call: If your problem can’t be solved, email for a phone appointment. Acknowledgements Much of the content in this document is original. Rather than reinvent content, some parts are based on content from other excellent sources and are hereby acknowledged. R.G. Keen’s site www.geofex.com - Tube Amp FAQ, Tube Amp Debugging AX84.com site www.AX84.com - Gary Anwyl's P1 construction guide version 1.0 GM Arts website http://users.chariot.net.au/~gmarts/index.html - Guitar Amp Basics Aron from diystompboxes.com Parts © Trinity Amps 2005. No part of this document may be copied or reprinted without written permission of Trinity Amps or contributing authors listed above. Version 3.2 Page: 5 WARNING Please Read this Information Carefully The projects described in these pages utilize POTENTIALLY FATAL HIGH VOLTAGES. If you are in any way unfamiliar with high voltage circuits or are uncomfortable working around high voltages, PLEASE DO NOT RISK YOUR LIFE BY BUILDING THEM. Seek help from a competent technician before building any unfamiliar electronics circuit. While efforts are made to ensure accuracy of these circuits, no guarantee is provided, of any kind! USE AT YOUR OWN RISK: TRINITY AMPS EXPRESSLY DISCLAIM ALL LIABILITY FOR INJURY OR PROPERTY DAMAGE RESULTING FROM THIS INFORMATION! ALL INFORMATION IS PROVIDED 'AS-IS' AND WITHOUT WARRANTY OF ANY KIND. REMEMBER: NEVER OPERATE YOUR AMP WITHOUT A LOAD. YOU WILL RUIN YOUR OUTPUT TRASNFORMER! Version 3.2 Page: 6 Version Control Version Date Change 2.0 1 Oct 12 New issue for New board & layout 2.01 6 Oct 12 Added 240V Transformer Wiring layout 2.1 16 Jul 13 Updated BOM; Note on transformer mounting added. 2.2 8Mar14 Note added to test PT AC voltages before proceeding. 2.3 9 Jun 14 Clarified start up procedure with numbered steps. 2.4 6Aug14 Added HI Capacity PT and 8/4 Ohm OT 2.5 28Jan15 BOM Updated, Added Optional PI resistor; clarifications mad; input jack theory added 2.7 15Jan16 Updated BOM to reflect IEC socket & Impedance switch 2.8 6Feb16 Updated for IEC socket wiring 2.9 8Mar16 Updated for IEC and Impedance Switch additions. 2.91 28AJul16 Updated layout for Mods section to show correct orientation of input jacks 2.92 23Apr17 Updated BOM 2.93 19Dec17 Updated eyelet board layout ; added power transformer testing section 2.94 4Mar18 Updated ‘Running 6L6 Output Tubes’ section 3.0 19May18 Updated for new Power Transformer 9114-2-EX connections 3.1 14Jul18 Updated Running 6L6 Output Tubes 3.2 25Aug18 Updated 240V layout picture Version 3.2 Page: 7 Guitar Amplifier Basics Electric guitarists can be fairly criticized for their reluctance to change to new ideas and technologies; however, there is no doubt that a classic 1950’s guitar and tube amplifier in good condition still sounds great in modern recordings. This is a testament to good design from the start. What has improved today is consistency, and the cost benefits of production line manuFacture. This is offset by the rarity of good guitar wood (it makes a huge difference, even on an electric guitar), increased labour costs for both guitars and amplification equipment, and the availability of good and consistent quality tubes. There is also an element of nostalgia, with memories of many of the great players of years gone by, and the desire to use the same types of instruments and equipment to recapture the magic. Vintage instruments and equipment have also become valuable collectors items (some with very inflated prices) which adds further to the desirability of older tools of the trade. There has been a recent trend by many companies to re-market their original instruments and equipment; new guitars can even be bought now ‘pre-aged’! This desire for vintage equipment is also related to guitarists’ reluctance to part with tube amplification, and there are many reasons why tube and solid state amplifiers behave differently. Quite simply, if players prefer the sound of tubes, they will continue to buy and use them. Here are some fundamentals. Input Impedance Typically 1M, 500K minimum (humbucking pickup guitars have volume pots up to 500K, single coil pickup guitars typically of 250K) . Tone Controls Magnetic guitar pickups are inductive, and require compensation, although this opportunity is also used for tone enhancement, not just correction. Without compensation, they have a strong low middle emphasis and little high frequency response - overall a very muddy and muFfled sound. This is why typical hi-fi Baxandall treble & bass controls are unsuitable. To hear the natural sound of a pickup, use a typical guitar amp with the middle set to full, and bass and treble on 0. This is actually sets a flat response in the amp (see below). Expect to hear a muFfled and muddy sound. And that's the whole point of these tone controls providing compensation for the natural sound of a pickup - the middle control simply boosts the pickup's normal ‘middley’ sound. The treble and bass controls do the opposite - they boost higher and lower frequency levels, leaving a notch in-between for middle cut (see the Fender/Marshall comparison below). So with typical settings of a bit of bass, middle and treble, the overall tone equalization complements the natural pickup sound for a balanced response of lows, mids and highs. Version 3.2 Page: 8 Full middle boost with no bass or treble actually gives a near-flat frequency response, allowing you to hear the natural sound of your pickups. Fender and Marshall tone controls Here are circuit diagrams of typical Fender and Marshall tone controls. They both meet the criteria of compensating for pickups' low-middle emphasis, as well as providing a useful range of tone adjustment. The Fender and Marshall circuits are each tailored to suit their own styles, which are quite different. Although a generalization, Fender's market and consequently the power output stage are geared towards provided clean and chunky tones at clean and early-overdrive levels. Marshall amps are best at low-middley and crunchy rock tones, played at medium to high overdrive levels. Here is a simple comparison of Marshall and Fender response with what might loosely be called 'typical settings' of Bass on 3, Middle on 4, and Treble on 6. The most obvious difference is that the Marshall lets more level through, and their tone controls have less range of adjustment. The higher level means that by using the same number of preamp tube stages, a Marshall can overdrive the output stage more. Version 3.2 Page: 9 Bearing in mind that 6-string guitar notes don't go below 80Hz, and typical guitar speakers cut above about 5KHz, these responses are similar. Both have a middle dip that is primarily compensation for typical pickups' middle emphasis, rather than an obvious dip in middle response. The Marshall circuit has this cut about an octave higher than the Fender, leaving the low mids and bass intact for that full Marshall sound. On the other hand, Fender's tone controls allow high-mids to pass with the treble response, and add little bass boost for the sparkling and tight sounds they're famous for. Here are charts each of the Fender controls. In all cases, the other two controls are left at 5. For example, the treble chart shows he effect of varying Treble from 0 to 10, with Bass and Middle both at 5. Notice that all controls have a wide range of adjustment, and that the bass control has most effect from 0 to about 3. Anyone's who has used a Fender will know this, and this control could easily be replaced by a control with a stronger logarithmic taper to smooth this out without changing the range of available tones. Version 3.2 Page: 10