The Airtight Garage – home

Information, history and the fine print

About Us

TheAirtightGarage is a small company that hand makes custom guitar amplifiers and guitar speaker cabinets. TheAirtightGarage does not clone, copy, or otherwise “recreate” old amps as many people seem to be doing as of late. TheAirtightGarage creates each amp individually as a new design. If you are looking for a clone or recreation, we suggest searching Google or some of the guitar amp forums for advice on a builder who will do that for you.

FAQ

I ordered a board kit and lost the paperwork! HELP! (or general help on installing board kits)

First, the layout diagrams are all on el34worlds site, under Hoffman Board information. Secondly, the info on wiring input jacks, etc is also on that page under Common Hookup information. You can also read the Tips for Board install paper on my site.

Are all of your amps handmade?

Yes, the cabinets and the circuits are all handmade. However, some chassis are pre-made for TAG, and some are not.

I ordered my amp, when will I get it?

It depends. I will always give an approximate time to deliver when you order your amp, or if you call beforehand I will give you an estimate. Due to the fact that they are all handmade, it will take some time for your order to ship. Bear in mind, I am a one man operation. Your amp will be built from start to finish by myself and if I have a lot to build, well it will take a little longer. It is well worth the wait, however. See the reviews on Harmony Central for customer comments.

Are any of your amps recreations, or copies of vintage amps?

No. At one point some amps were modified vintage circuits, but this is no longer the case. If any circuits “look” like a vintage circuit it is due to the fact that there are only so many ways to hookup a tube in a curcuit. The redpeppers output section for instance “looks” like a two tube champ, but this is because there are only a few ways to hookup a single ended parallel pair of tubes, and for max power, it is standard pentode configuration like a champ output. We could argue that 99% of every amps preamp “looks” like some other one as there are only a few ways (many, but only a few used in guitar) to hookup a triode, for example.

Which (brand of) capacitors do your board kits come with?

The capacitors used in the board kits (under circuit boards) are chosen for maximum performance for a variety of styles. I have found over the years that the setups that I am using are the ones that most players like the most. Typically, Mallory M150s in the front end (preamp section, tone stack(s)) and Xicon MPP in the rear are a great combination. Spragues are ok, I find them not as good as the Xicons, actually. I do put a sprague in certain positions on certain board kits, however.

Can I order a board kit with just the turret board and no parts?

Yes, you can order the board kit with just the turret board. As of the writing of this FAQ, it should be an option on the website.

I want to assemble the board kit myself, can I order the kit with no parts installed?

Yes, but with a clarification. I will NOT sell you an undrilled board with the turrets NOT installed. I WILL sell you a board kit with the parts (capacitors, resistors, etc) not installed, however. This is due to the fact that some people want a modfiied board, so they order it with no holes. Problem is, if they mess up, guess what? Yes that is correct, it is all my fault, even though I never touched the board. Sorry, but I am too busy to have to deal with such items that are not my fault. I will help you via email and phone with a board kit, but not one that you have modified. If you want a “custom” board kit, email or call me for a quote, you may be suprised to find I do not overchage you for it, as I have been doing this for a long time, and it does not take me long to make a layout for you.

Why do the power supply capacitor boards no longer come with Sprague ATOM caps?

They are not the same as they used to be. In fact, there are two reasons for the non-use. First, Vishay/Dale tells you in the spec sheet not to use them on new installs. If the manufacturer telling you not to use them is not enough, the second reason is that they are not the same cap. If you cut one open, you will see that the cap inside is actually a much smaller cap just put into the big blue can. This is due to the fact that they are using them as a drop in replacement for older equipment that has the old spring clamp. They are in fact using a new capacitor on the inside... so why pay 100% more for the same cap? Instead TAG uses the F&T from Germany, the Tube Amp Doctor caps or the IC for general purpose use.

Can I put the AB763 board into my reissue _________?

See this page and scroll down to the AB763 for more information.

What does the cap upgrade on the board kits do? How will it sound? Do I need it?

The upgraded capacitors on the board kits changes out the capacitors in the front end (preamp, tone stack) to “hifi” caps for lack of a better word. The capacitors are of improved quality and construction. I normally advise against this unless you are a jazz player, as it will make the amp much more transparent. You need this if you really want a transparent amp. Think plugging it into the mixing console kind of sound.

Do you have export models?

Yes, there are export models of all amps, however, there will be an additional delay in building the amp and an upcharge as the transformers are custom wound (nearly all of them are anyway, but another special order will have to be made for it).

What transformers are used in TheAirtightGarage amps?

It depends. Most power transformers are custom wound or they are hammonds or vintage iron. Output transformers on the small amps are Hammonds. If you would like to know what is in a particular model, ask us.

What tubes do you like to use in your amps?

That is a loaded question. It depends. Even when I have picked a tube, sometimes I receive a bad batch and have to thrash all of them. If you are going to purchase an amp and would like to know what will go in that model, use the contact form to send the question.

Which tubes will sound best in my super-duper-reissue-maxi-blaster?

None. Take it outside, shoot it, burn it, attend therapy to forget you ever played that horriffic sounding load and buy an AirtightGarage amp.

What is the power difference between amps built with 6V6s or 6L6s or EL34s or EL84s or 6550s or 7868s or 300Bs or 811s or ???

In the end, it is how the designer built the amp... is this push pull, single ended, (or parallel on any of those, or parafeed on top of that), triode mode, pentode mode, conservative design, maximum rating design, etc? The list goes on... It is really up to the designer in the end. For example, the Nora amp is two 6L6 tubes in class A push pull at 20W. The upcoming “in the trunk” amp is two 6L6 tubes in class AB1 push pull for 45W. Finally, take what the designer/builder says with a grain of sand. You can not consistently tell power output by listening. You also can not trust what the designer tells you all of the time. Sex, lies and output power were really really bad in the late 70’s through the 90’s. I have seen 20W solid state amps being touted as 150W amps, and they could get away with it due to the method of measuring output power (change the conditions and you can change the power dramatically). At TAG, power measurement is first calculated (output power - transformer losses) and them measured with pink noise limited to the guitar range plus or minus one octave of harmonics into a reactive load at mad volume. Thre are a thousand ways to measure output power, but I feel that one is probably the most “honest”. Again, you could change the tubes out and get more or less power out of the amp, so don’t call me a liar wen you change your tubes and get 1W more out of the amp.

You claim the Nora is class A, how can it be class A with two 6L6 tubes and deliver 20W of power!?! Some guy I do not know on some forum somewhere said that is not possible! You are a stinking liar!

Sigh. I get this a lot, and it is due to a lack of knowledge, or more commonly, the spread of disinformation. I could spend a long time talking about this question, but instead I will just point out a few things here. A lot of amp builders want you to belive that class A is only for single ended amps, or only for cathode biased amps or only for their new amp they just came out with. Truth be told, you can have a class A amp in ANY configuration (single ended, parallel, parafeed, etc) using ANY bias method you choose (fixed, adjustable, cathode, whatever). The real problem lies in that most companies bend the truth about class A (mostly since they either do not know or it is a marketing gimmick). The classic example is the VOX AC30, which is NOT class A. In fact IIRC a magazine stated it was class A at first, then VOX did, or something like that. It does not meet the definition of a classsA amplifier. See this great explination for more details. To add even more confusion to the mix, there are a great number of technicians in the wild who will state, quite confidently, that their amp is class A up to a point. While this may be, in a certain sense, true (it all depends on lawyer speak and whose definition of class A you are using), I feel it is a bad way to state the class of operation of an amplifier. If we go by that method (class A up to a point) then with the exception of a very very few amps, all amps are class A, so why even bother making a distinction? Lets just say they are all class A and get it over with. Well, die hards like myself do not do that, as there is a real distinction, and in guitar land it usually happens near the end of the volume control, where most of us like to play. 99.999% of those “class A” amps will no longer be class A there, and that is where it matters most, is it not? In the end if you still think I can not get that kind of power in class A from two 6L6s, well, you could always grab the spec sheets and curves, choose the operating point, draw the loadlines, do the calculations, build it and verify it...but I have already done that for you. Your welcome.

You claim the Nora is only 20W, but I played it at (a friends house, dealer, your shop) and it seems like it is a lot louder than my (20W, 30W, whatever) I have at home. You are lying about the power!! Why is it louder if it is only 20W!?!

Again, I get asked these questions a lot, and there is a simple explination. Speakers can make a huge (and I mean huge) difference in sound pressure level with no change in the amps power. If I have a 15” driver that can do 100db at 1W (2.83V) at 1m and am driving it with 1W, its “kind of” loud (is that technical enough for you?). If you have an amp with a 15” that can do 94db at 1W (2.83V) at 1m and you are driving it with 1W it will seem a LOT quieter. In fact it will _seem_ like I reduced the power of the amp to 1/4W. There are many places on the internet and in texts which will go much more indepth on hearing, sound pressure in air and the db scale. I will not bore you with the details here but be careful to watch out for opinions vs fact when reading about it online.

Some of your amps use 15” speakers (the Nora, the old Betsy, and a few others), why would you use a 15” speaker? Don’t they suck or they are boomy?

It all depends on which 15” you use, and how you use it. Personally I like 15” speakers, but in reality, when I design an amplifier, in the back of my mind I am thinking about the overall sound of the amp, what kind of response and tone I want out of it. To that end, the speaker choice is all about tone. The nora uses a 15” to get that tight, big nasty low end. It has guts and low end for miles, but only 20 watts, so you are not killing people with it either.

Warranty

TheAirtightGarage Limited Warranty

Terms and conditions

Limited Warranty. TheAirtightGarage warrants this product to be free from manufacturing defects in material and workmanship, subject to the conditions set forth in this warranty, for a period of five years from the purchase date of the product, except for vacuum tubes which are warranted for ninty (90) days.

Exclusions. This warranty excludes vacuum tubes (after 90 days) and pilot lamps (after one year).

Limitations. This warranty is subject to the following: The warranty is void if the product has been used, handled or installed in a manner other than in accordance with the instructions in the owner’s manual, abused, damaged by accident, neglect or in transit, or damage due to repair, disassembly or modification by anyone other than TheAirtightGarage. When returning products to TheAirtightGarage, the product must be packed in the original shipping container, and returned to TheAirtightGarage at the owners sole expense. TheAirtightGarage will pay return freight of our choice, within the continental United States of America. All returned products must include the serial number of the product and a description of the defect.

Repair. TheAirtightGarage will repair or replace any defective parts, which fall under the guidelines and condition set forth in this warranty as they see fit.

Misc. The warranty does not extend to any incidental or consequential costs or damages to the purchaser.

Shipping Policy

We ship worldwide. Every amp and cabinet is handmade to order, so ship dates vary with the build queue; we’ll give you an estimate when you order.

Export models for other mains voltages are available, with extra build time and an upcharge for the custom-wound transformers. For shipping quotes, availability or special requests, please get in touch.

End of Life

This page will describe the amplifiers that have been end of lifed here at TheAirtightGarage. These are mostly in order of appearance.

Emily

Emily

The Emily was not the very first amp made here as a company, but was one of the first offered. It was like a deluxe, but had more headroom, and did not fart out at the end of the dial. It also had a lot more articulation and accuracy. The unit was tweeded, then aged, and the faceplate was aluminum or brass that was engraved with a pantograph machine. MSRP was $1200, they sold for about $800 in store.

Betsy Tonebuster

Betsy Tonebuster

This was a 4x10 55W amp that was sortof a modded bassman. It sounded like a bassman at low volumes, but again, when cranked it did not loose articulation, accuracy, transparnecy, etc. It did not give up at high volumes like so many amps based on this circuit did. It was this amp which made TheAirtightGarage give up on any sort of modded version of any amp. Basically, this amp was on stage at a blues jam, and a guitar player next to me leans over and says “That bassman is the best amp I have ever heard in my life, I am going to go pick one up tomorrow at (store name deleted)” and walks off before I can open my mouth. At that moment it was decided that we shall have no tweeded amps and that our amps were going to all be all original designs. MSRP was someting like $1900 or thereabouts (it had custom iron in some and very expensive caps). They ended up selling for around $1200-$1500 in person. Here is serial number two IIRC...

Betsy 115

Betsy 115

This is almost the same amp as the Betsy, but there are a few small changes. The amp itself has more clean headroom. It is also even more transparent. This was done by using custom power and output transformers in the amp and som esmall circuit changes. It also used one 15” driver instead of four tens. This amp was more of a jazz/country amp, but several rock guys like it due to the clean power that it had.

Zoe

Zoe

The Zoe was another in the tweed series of amps, this one had three ten inch drivers and was very low power (20W). One could think of it as a modded bandmaster type amplifier. Again, this was in the tweed craze era (even though it was a mere 2 years into it when we stopped all of this tweed amp business) and it sure looks like a clone.

Bunny

Bunny

The Bunny was made about the same time as the Emily and Betsy. It was another modded classic circuit that we moved away from. It was a 6W or 10W single 8” or 10” amp in tweed. Single volume control, later on we built a MKII which had vol/tone and either 5, 10, 12 or 18W of power (two output tubes and you could mix/match/swap them). MSRP was $600 but they sold for less.

The Barbara

The Barbara

This was a modified reverb vibrato unit. This is a really nice analog reverb and vibrato unit. It is based on the “Hoffman” Revibe unit, which has been changed by a guy in Norway to a tremolo unit. We sold very few of these, but the ones we did sell satisfy the customer to this day.

Candy

Candy

The Candy amp was one of our most original amps ever. Nothing about this amp was based on any amplifier or cicuit that we know of. This was a two channel amp (one clean and one mean) that had two completely separate preamp circuits. Each pramp had its own tone stack, volume, master volume and reverb unit (each with its own tank). It had 45 watts of power, eight tubes in the preamp section and three tens. You could use the clean channel or the mean channel or both at the same time, which gave you such an immense possibility of tones that it is hard to even describe. You had clean, mean, crunch, distortion, and everything in between and reverb on each. This is my personal favorite amp of all time, and it took over a year to design and tweak it. The main fault of this amp is its price. There is so much circuitry in this amp that it is cost prohibitive and only a handful of customers can really afford it. MSRP was $2100.

Tube Thoughts

Thoughts on tube replacement, picking tubes, and bias in TheAirtightGarage amps.

Read Tube Thoughts

A Short History of the Vacuum Tube

Every amplifier we build rests on a century of tube development. Numbers in superscript refer to the sources below; patent numbers are those given in those sources.

  • 1873–1884Frederick Guthrie reports thermionic emission (1873). Thomas Edison, working on the light bulb, observes current flowing from a hot filament to a separate plate in a vacuum, the “Edison effect”, and is granted a patent in 1884 for using it in an electrical indicator. He finds no further use for it. 12
  • 1904–1905John Ambrose Fleming, a former adviser to Edison’s London company, applies for his “oscillation valve” patent on 16 November 1904. He uses the Edison-effect bulb as a radio-wave detector. British patent 24,850 is granted on 21 September 1905, and his US application issues as patent 803,684. The US patent was later ruled invalid. 234
  • 1906–1908Lee de Forest adds a third electrode, a control grid, between filament and plate, creating the Audion, the first triode. Robert von Lieben of Austria independently patents a three-element tube in 1906. De Forest’s US patent 879,532 (filed 25 October 1906) was granted on 18 February 1908. 56
  • 1912–1913Researchers recognise the Audion’s ability to amplify. By 1913, higher-vacuum triodes are built by Harold Arnold at AT&T and by Irving Langmuir at General Electric (the “Pliotron”), making tubes stable and dependable. 5
  • 1916–1927Walter Schottky invents the tetrode (1916), adding a screen grid. Albert Hull’s screen-grid tube patent was filed in 1925 and granted in 1927. 68
  • 1926Bernardus Tellegen and Gilles Holst at Philips develop the pentode by adding a suppressor grid, which cures the screen-grid tube’s secondary-emission problem. Tellegen’s US patent was filed 11 June 1926 and granted 30 January 1934. 578
  • 1933–1936Engineers at EMI in Britain (Isaac Shoenberg, Cabot Bull and Sidney Rodda) patent the beam power tetrode (GB 423,932, published 1935; US 2,113,801). In April 1936 RCA introduces the 6L6, the first successful beam power tube. The 6V6 and Britain’s KT66 follow, and these tubes become the standard output tubes of musical-instrument amplifiers. 910
  • 1950s–todayTransistors replace tubes in most radios and televisions by the 1970s. Tubes remain in use in high-power transmitters, high-fidelity audio and, above all, musical instrument amplifiers. 15

Key tube patents

PatentInventorSubjectDates
1884Thomas EdisonElectrical indicator using the “Edison effect”Granted 1884 24
GB 24,850J. A. FlemingThermionic (oscillation) valve, two-electrode diodeFiled 16 Nov 1904; granted 21 Sep 1905 3
US 803,684J. A. FlemingSame invention, US patentApplied 16 Nov 1904; issued 1905 23
US 879,532Lee de ForestAudion triode, control gridFiled 25 Oct 1906; granted 18 Feb 1908 6
(see source)Albert W. HullScreen-grid tetrodeFiled 28 Jan 1925; granted 6 Sep 1927 6
(see source)B. D. H. TellegenPentode, suppressor gridFiled 11 Jun 1926; granted 30 Jan 1934 6
GB 423,932Shoenberg, Rodda, BullBeam tetrode, “improvements in thermionic valves”Published Feb 1935 9
US 2,113,801Shoenberg, Rodda, BullElectron discharge device (beam tetrode)Published Apr 1938 9

A Short History of the Guitar Amplifier

The electric guitar needed a tube amplifier almost from the day it was invented. The timeline follows the key inventions, patents and amplifiers.

  • 1920sMakers try to make stringed instruments louder mechanically with resonators (for example Gibson’s 1925 banjo resonator, US 1,678,456). Lloyd Loar at Gibson is said to have built early pickups in the early 1920s. 1112
  • 1931–1932George Beauchamp and Adolph Rickenbacher found Ro-Pat-In (later Rickenbacker). Their electromagnetic pickup is fitted to the cast-aluminum “Frying Pan” lap-steel guitar, widely regarded as the first mass-produced electric guitar, sold with companion amplifiers from 1932. 111314
  • 1936–1937RCA’s 6L6 and the 6V6 give amplifier builders a rugged, efficient output tube. The 6V6 soon turns up in combo guitar amplifiers such as the Gibson GA-40 and Fender’s Champ, Princeton and Deluxe. Guy Hart’s Gibson pickup patent (US 2,087,106, the “Charlie Christian” pickup) issues on 13 July 1937, and Beauchamp’s patent 2,089,171 (filed 2 June 1934) issues on 10 August 1937. 91215
  • 1939–1941Laurens Hammond files a patent on 15 July 1939 for an “electrical musical instrument” using a spring to add reverberation. It issues as US 2,230,836 on 4 February 1941 and is the ancestor of the spring reverb tanks later built into guitar amplifiers. 1617
  • Late 1940sFender amplifiers such as the Super use the 6L6G output tube, and the Bassman later uses the 5881, a ruggedized 6L6 variant, helping make the 6L6 family the classic American guitar-amp output tube. 23
  • 1958–1959In Britain, Dick Denney designs the EL84-powered Vox AC15 (1958), often billed as the first tube amplifier designed specifically for the electric guitar. Popular with The Shadows, it is followed in 1959 by the louder AC30, built at the band’s request and in answer to the more powerful Fender Twin. 1819
  • 1962–1963London shop owner Jim Marshall, with repairman Ken Bran and engineer Dudley Craven, prototypes an amplifier in 1962 as an alternative to imported American Fender amps. Production of the JTM45 begins in 1963, named for Jim and his son Terry Marshall and its 45 watts. The circuit mimicked the Fender Bassman’s, in an all-aluminum chassis. 20
  • 1961–1963Hammond licenses its Type 4 spring-reverb tank to Fender, which uses it in the 6G15 Reverb unit (1961). In 1963 the Fender Vibroverb becomes the first guitar amplifier with built-in spring reverb. Vox builds its own tank with a different design, reportedly to avoid licensing Hammond’s patent. 172124
  • 1966 onwardVox and others introduce solid-state amplifiers, yet tube designs remain the benchmark for tone, and many modern builders, including hand-wired boutique shops like ours, continue to work with them. 22

Key guitar-amplifier-related patents

PatentInventorSubjectDates
US 1,678,456GibsonResonator for banjo, an early attempt at louder instruments1925 11
US 2,089,171George D. BeauchampElectromagnetic pickup: the “Frying Pan”Filed 2 Jun 1934; granted 10 Aug 1937 1213
US 2,087,106Guy Hart (Gibson)Pickup used on the EH-150 (“Charlie Christian” pickup)Filed 8 Feb 1936; granted 13 Jul 1937 12
US 2,230,836Laurens HammondElectrical musical instrument with spring reverberationFiled 15 Jul 1939; granted 4 Feb 1941 17
US 2,573,254Leo FenderBridge and pickup arrangement later used on the Telecaster1950 11

Dates of early pickup and amplifier developments vary between sources; where they disagree, we have given the date on the patent record or the most widely cited one.

Sources