Ask Amp Tech Expert Skip Simmons

I often see vintage amps with plenty of new caps, new tubes, etc., but they still don’t sound or work right. Why? Because good servicing is the first investment you should make, not the last. I know it's tempting to "just give it a cap job and a set of tubes," but that's like putting a new engine in your 1964 Chevelle when all you really needed was a fuel filter!

Skip Simmons

"XYZ Brand tubes will radically improve the tone of your amp!"

Different tubes of the same type CAN sound different, but expecting dramatic, life-changing "improvement" by using a certain brand of tube will prove disappointing. One exception that applies to harp amps is substituting a lower-gain preamp tube for the stock tube. This really can make an amp easier to play by reducing the gain, especially in a high-gain circuit like the tweed Bassman.

Skip Simmons

Skip Simmons Harp Amps

"If you connect your 8 ohm amp up to a 4 ohm cabinet, you will blow your amp up!"
Not true..... A speaker impedance mismatch of up to 100% (up or down) will not hurt a quality tube amp, so relax and experiment a little. Try two 8-ohm speakers with your Deluxe, or run that tweed Champ through an old 8 ohm P12R and be amazed! I know some pros who deliberately mismatch the speaker/amp impedance because they prefer the tone.

Skip Simmons

Internet nonsense #1. "Tubes can be damaged by oil from your skin, so never touch the glass." Just think what a radio operator in WWII would have thought of that advice! He would have been laughing his head off.

Skip Simmons

Skip Simmons Harp Amps

Greetings! I not so recently inherited the above mentioned peavey VT 100 amp. It was gone through, but not necessarily with a harp in mind at the time. Speakers were replaced with 2x12 celestion vintage 30's and it has 2 6l6 tubes. Is there anything I can do to make this amp more harp friendly as far as tubes or anything else? I do like the phase and spring reverb. The sound is pretty decent when plugged into the auto mix jack but a little to clean and sharp in the normal jack 1 or 2. continue reading...

OK, this is an obvious tip, but easily overlooked. Mic cord is shielded, but speaker cord is not. Using a speaker cord on your mic will cause intense noise due to the lack of shielding. Using mic cable in place of speaker cable can make the speaker sound blown or even cook an output transformer, so check those cords to be sure of what you have.

Skip Simmons

Skip Simmons Harp Amps

I need to replace the power tubes in my Harp King 6x10 (KT90) . I have two matched tubes that show a bias point of 37. I have no idea what the original tubes bias point was and it does not appear that John has a point on the chasis for the bias to be adjusted. I have no tech ability, but my bass player has extensive background with all tech aspects. Just hate to let him touch it until I get a little more info. Have an email in to John Kinder, but getting in touch with John can often take some time.
I don't want to hurt this amp - can't go to the local music store to get a replacement. continue reading...

Sometimes you run into a pot where the shaft is frozen to the body of the pot. Recently I had a vintage Masco with this problem. The original pots always work better than new ones, so I really wanted to save it. I tried everything I could think of, including electronics cleaner, WD-40, Cramolin, brake fluid, etc. with zero success. The answer was rubbing alcohol. It takes some time, but if you work the alcohol into the space between the shaft and the bushing while gently trying to turn the pot, it will come loose. Thanks to the legendary Earl Yarrow of Newman, California for this tip. continue reading...

The shielded cables that connect the reverb springs to the amp are a weak link on many classic Fenders. The RCA plugs on both ends of the cables need periodic cleaning and tightening. Always check these cables first if your reverb is dead or noisy, even on a newer amp.

Skip Simmons

Skip Simmons Harp Amps

G'day Skip,

I have a Vibro Champ XD. I notice it has 2 jacks in back. 1 is marked 'line out', the other 'speaker out'. what is the difference here? does the 'line out' come from the preamp stage, bypassing the power stage?

on the subject of this 5w amp, i'm wondering how much speaker it could drive. do you think a pair of 10"s would be beyond it?

Thanks,
Dave