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The JT30 FAQ

Astatic JT-30 Frequently Asked Questions.

Astatic has made the JT-30 Microphone for over 50 years. It started as a microphone for Ham radio base stations and then became the Ford of microphones. It was cheap, rugged, and everywhere. The Microphone was the standard in radio communications for the second half of the 20th century.

When Muddy Waters started popularizing Amplified Blues in the late 40’s and early 50’s, harmonica players looked for a way to amplify their instrument. Little Walter Jacobs and others found that the JT-30 fit nicely in their hands, and lent a raw horn like tonal quality to the harmonica, and was easily found. The JT-30, with its limited frequency response, took the harmonica with its cheap reeds, from a child’s toy to an expressive and responsive instrument. By not responding well to higher frequencies, the JT-30 cut out the reedy tones of the harmonica and passed on the deeper vocal qualities of the instrument.

When Little Walter recorded “Juke” with Muddy, he made the microphone and amplifier almost as much an instrument as the Harmonica. The JT-30 has been the standard Amplified Blues Harmonica ever since “Juke”.

Questions:

Q. I have a CAD HM50 or Hohner Blues Blaster. It looks and sounds like a JT-30. What’s the difference?

A. The Astatic JT-30 is manufactured today with only minor changes from the ones produced over 50 years ago. It is branded as the Hohner Blues Blaster, The Astatic JT-30 and the CAD HM50. All are the same microphone with small cosmetic differences. The Blues Blaster has the Hohner label instead of the Astatic one. CAD is a division of Astatic and is the same mic with a gold tone grill.

Q. How much is my JT-30 worth?

A. Not much. Astatic still makes the JT-30 and in the past 50 years have made millions of them. The JT-30 shows up regularly at garage sales, flea markets and junk stores. I never pay more than $35 for a mic. You can buy a new one for under $80. You can buy a mic in good condition with a stand on Ebay for $50 to $100. Old mics with the Astatic Laboratories logo will go from $100 to $200 depending on condition and the type of stand.

Q. How old is my Mic?

JT-30’s have been in constant production since WW-II. Astatic has not been concerned with collectability of the JT-30 and would rather that you buy a new one. They don’t have any records of the serial numbers (at least not that they will tell me). Astatic Laboratories microphones appear to be late 30’s early 40’s. The JT-30 may have been first produced in 1937-39 in a period when Astatic was branching out to a variety of microphone and phonograph pickup solutions. They produced microphones for World War II and the Brown Astatics with the Astatic Laboratories label are from this period.
Some time in the mid 1940’s, Astatic moved to Conneaut Ohio where they are still located. The name of the company changed to Astatic Corporation.
The gray hammertone mics are often from the 50’s and 60’s. The earlier mics have a Patent Pending stamp on the label. Then the labels say Patent Numbers inside. In the late 50’s and 60’s the label has a patent number on the label and no serial number. The gray paint appears almost greenish brown on the older mics.
For a period, which appears to be the late 60’s and early 70’s, the label disappears and the body of the mic is stamped with the name Astatic. The gray hammertone disappears sometime during this time and the flat black paint is standard. There is also a flimsy two-prong plug, which replaces the ½ inch Amphenol microphone connector.
The blues revival of the 60’s, which included Paul Butterfield and others, increased the demand for the JT-30 and it was marketed through Hohner in the 1980’s as a musical microphone for harmonica. The JT-30 was produced with Volume control and then with a standard XLR cable connection.
I have seen mics with gray hammertone, greenish hammertone, army brown, olive drab, flat gray and flat black paint. I have seen chrome versions of the mic, but the end user probably chromed these.

Q. Where do I get a JT-30?

A. You can buy them in many music stores as Hohner, Cad or Astatic for $75 to $120 depending on the discount. On-line, you can get the Hohner Blues Blasters from www.Coast2CoastMusic.com/ at a good discount.
You can get the vintage mics on Ebay very cheaply or if you want a special one, Tom Ellis has some at Tom’s Mics at www.island.net/~blues/tomsmics.html, but be warned – these aren’t cheap! Then again, you get what you pay for.

Q. My JT-30 doesn’t work, what can I do?

A. The crystal element in a JT-30 is fragile. If you drop it, it breaks. You can get a new crystal at along with instructions on changing it. Angela Instruments and Kevin’s Harps also sells replacement elements. It’s easy to change the element. You need a screwdriver and a soldering iron.

Q. What are “Crystal Balls”, “Hot Rods”, “Cherry Bombs” and other microphones that look like JT-30s?

A. These are modified mics. Mic techs take a mic and add a Volume control or a rollover capacitor and the mic has a different tonal response. Sometimes they paint or chrome the mics. They are very cool, but the sound comes from within you and you may or may not sound better with a modified mic.

Q. I have a JT-30. How should I care for it?

A. Keep it warm and dry. Don’t drop it. Don’t leave it in the car trunk if the temperature is going to go below freezing. Don’t leave it in the car on a hot day. Keep it clean, but don’t get it wet. Dry your spit off the face after you use it. Don’t loan it out to drunks. When you set it on your amp, make sure that it won’t roll off.
Store it in a cheap, foam padded nylon handgun bag, available at gun stores (everywhere in the US) for about $3.

Q. What is the difference between a JT-30 and a Shure Green Bullet?

A. The JT-30 has a Magnesium alloy shell that makes it lighter than the Shure Green bullet. Some people find it easier to play the harmonica with the lighter microphone. They both seem to fit well in you hands. The JT-30 is definitely a dirtier sound, with an element that has few highs. The Green bullet can get the horn like tone that the JT-30 has because the harmonica is held so close to the mic that it overdrives it. You can also get clean sound out of the Shure mic, but using les air through the harmonica.
It’s a matter of what you prefer and what you are used to as to which mic you think is better. Good harmonica playing starts with the player and the main use of the mic is to make you louder.
The Green bullet uses a “Controlled Reluctance” element that is a magnetic element. It can give you a better frequency response. The older elements seem to have a smooth, buttery sound (very subjective) as compared to the newer Mexican elements in the mics made now. The element in an old Shure can be worth more than the mic.

Q. I have a JT-40, JT-50, JT-30VC, W-80, etc. What is the difference between it and a JT-30?

A. Astatic made different versions of the JT-30 using the same Shell for a variety of applications. They are all the same mic with different paint jobs or different elements. Since very few original elements survive over the years, it is unlikely that the difference means anything any more.

Q. I want to replace my blown element with a new one. I see I can buy a crystal element or a ceramic element. What is the difference?

A. Astatic now sells a ceramic element (MC-127) that is harder to break and yet very similar to the original crystal elements (MC-151). Little Walter used the crystal element JT-30 when he recorded and performed, but he had no choice. Gary Primich told me that he prefers the ceramic element because it as a little raunchier sounding. I am told that William Clarke used the Ceramic element. They sound so much alike that I can’t tell the difference. I can hear differences between individual crystal elements – two elements from the same batch can sound quite different, but I can’t tell you if an element is crystal or ceramic just by listening.

Q. When I opened my JT-30 the element had MC-101 on it. What element should I use to replace it?

A. Astatic has used several ways of identifying elements. The 101 is a crystal element and if you want to replace it you might use the MC-151 element which is also a crystal. The MC-127 is more rugged and a better bet for someone who breaks his mic every few weeks. The sound is very close.

Q. I bought a MC-151 element and it had 127 stamped in the metal and a sticker that said MC-151 on it. Did I get ripped off?

A. No. Astatic broke the 151 mold about 15 years ago and has been using the 127 mold for both ever since.

Q. The JT-30 is a high impedance mic. What does high impedance mean?

A. Impedance is a way to measure of electrical resistance. The JT-30 does not conduct electricity well and is therefore a high impedance device. When the JT-30 was designed, the tube amplifiers of the time needed an input that had high impedance. The JT-30 looks like a guitar to a guitar amplifier. Tube guitar amplifiers expect very high impedance as input and work best that way. Modern microphones are low impedance. They don’t need as much preamplification and require a small transformer that matches the impedance before they can be used with a guitar amplifier.

Q. My amp howls when I plug in my JT-30. How do I stop the feedback?

A. Turn down the volume on the amp.

Q. Is there anything else that I can do to stop feedback?

A. Many years ago I wrote an article on feedback. Read my article on feedback. Since then I found that you could replace the first 12AX7 tube (the one closest to the guitar jack or furthest from the power supply) with a 12AU7 tube. I am told that this doesn’t hurt the amp. The 12AU7 is a lower output tube and will limit you amp a little - make it less loud, but at the same time make the amp less sensitive to feedback. The effect is you can get a lot more volume out of the amp before it feeds back. I have tried this in a reissue Bassman and a Blues Deluxe and it seems to work.

Q. What can I do to improve my mic?

A. There are lots of things that go from cosmetic to major changes.
Cosmetic changes:

a. Paint it a cool color. I have been to the auto parts shops and hobby shops and found cool paints like “Candy Apple Red”. One of my favorite mics is now Red Hammertone. No one likes it except me, but I think it is way cool.
b. If you know a body shop or Motorcycle shop where they do airbrushing, the artist will do your mic up with cool flames or something. It is real small and a nice challenge, so with a little human engineering you can get the job for free.
c. The yellow pages in any medium size city should have a few places where you can get you mic chromed or nickel-plated.

Electronic Changes:

a. Change the element from crystal to ceramic or vice-versa. Find an old Shure mic and put the element in the JT-30. Find an old rotary phone and take out the old carbon receiver. Put that in the JT-30 (some of them fit nicely) – Diiiiiirrrrrty! Go to Mouser.com and buy the cheap 2-inch crystal microphone element. Mine only last a few days, but they are very nasty sounding.
b. Add or replace a volume control. Some of the VC mics have a 250K-ohm pot. Find a 1, 2 or 5-meg pot with a long neck and replace the smaller pot. This increases the total impedance of the mic. The more impedance, the less feedback and better sound.
c. Add a rollover capacitor. A 150-uuf capacitor across the pot (see the diagram at: /oldsite/piazza.html) can give you a little deeper tone. This may be superstition, but many players swear by it. If you don’t have a Volume control, put the cap right across the element and it will limit the mics response to very high frequencies and maybe limit feedback a little.

Connector Changes:

a. Get rid of the XLR connector and replace it with a short length of guitar chord ending with a ¼ inch female guitar connector.
b. Remove the old connector and drill a ½ inch hole in the place where it was. Be very careful or you can really mess up the mic. Put in a long neck ¼ inch guitar jack so the guitar chord plugs directly into the mic.
c. Put the Volume Pot at the tit end of the mic. This makes it easy to change the volume while you are playing.
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