ext speak question

way cool jr · **Joined:** Tue May 18, 2010 7:34 pm **Posts:** 6911

just over all poor design using substandard parts.

shimmilou · **Posted:** Sun Jan 02, 2011 12:03 am

Hi RVM lead,

Yeah, I could email Fender and see what they say, but I'm confident in my understanding of the subject. I don't know if we would get a tech answer, or a customer service answer though.

This is one of those things that just seems to be ingrained in all of our minds, "match the impedance", but I don't think that many people understand exactly why. In fact, a common test to check the turns ratio of a transformer, is to short the secondary, apply voltage to the primary and compare the current in the secondary to the current in the primary. But, you and the others have a good point, match the impedance rating of amp and speaker for the most power out of the amp (efficiency). But mismatched impedance within reason, will not harm the amp in the slightest.

Guitarist1983 · **Joined:** Sun Apr 06, 2008 12:07 pm **Posts:** 383

shimmilou wrote:

If you all are interested, here is a pretty thorough explanation of tube amp impedance, and matching of amp and speaker (link below). It does seem to be commonly accepted that impedance matching for an amp is important, and it is important, but simply for efficiency, in order to get the best sound and most power out of the amp. We all know that using a tube amp without a speaker will damage the amp, however, using the amp with a very low impedance speaker will not do any damage, even down to zero ohm load. Notice that many newer amps have a shorting output jack, so that if the speaker is unplugged, the OT will be shorted, which protects the amp from the "no speaker" condition. Here is an exerpt, it is about half way down the page on the site.

[i]"Q: What does the "impedance" of my output transformer mean?

...

http://www.geofex.com/tubeampfaq/tubefaq.htm#transformers

Thanks for this post. I learned a bit. I've read something similar, but much abbreviated, in Dave Hunter's Guitar Amplifier Handbook. He wrote something like 1/2 to 2 times the optimum load is not unreasonable.

http://www.amazon.com/gp/product/087930863X/ref=oss_product

IM4Tone · **Posted:** Sun Jan 02, 2011 7:29 am

way cool jr wrote:

just over all poor design using substandard parts.

Wondering why you purchased the BJ given your opinion of it?

way cool jr · **Joined:** Tue May 18, 2010 7:34 pm **Posts:** 6911

honestly, i didnt know it was made this way until i got on this forum.
i do love the looks and tone of this amp theres no question, but also know that it could have been built way better with quality parts. its almost like they said
"hey we have a bunch of spare parts, what can we do with them to get rid of them"
and we have the Blues jr.

IM4Tone · **Posted:** Sun Jan 02, 2011 7:47 am

I'd say if you like the looks and the tone and you're not having any reliability issues, it's a good amp until it goes bad. Remember that a lot of what is posted here is the viewpoint of an individual or two. That in itself doesn't make it fact. Hope you enjoy the BJ for many years and shimmilou's post has lessened (not quite eliminated) my concern for driving an ext. cab.

P.S. Regarding which external speaker: I like Celestions...the V30 or the G12H..or if the budget is tight, a Seventy80.

shimmilou · **Posted:** Sun Jan 02, 2011 7:48 am

Guitarist1983 wrote:

...Thanks for this post. I learned a bit. I've read something similar, but much abbreviated, in Dave Hunter's Guitar Amplifier Handbook. He wrote something like 1/2 to 2 times the optimum load is not unreasonable.

http://www.amazon.com/gp/product/087930863X/ref=oss_product

You're welcome.

If you don't want to buy the book, it is available on Google books here.

http://books.google.com/books?id=N9hAviH6gqEC&printsec=frontcover&dq=Dave+Hunter%27s+Guitar+Amplifier+Handbook&source=bl&ots=3DRWgns6aS&sig=wT0jKymSW5XSP-qznr8fj7CiWR8&hl=en&ei=sowgTezuC4P98AbrrY2eDg&sa=X&oi=book_result&ct=result&resnum=5&ved=0CEMQ6AEwBA#v=onepage&q&f=false

Edit:
It looks like some of the pages aren't available in the Google books version.

This may be the quote that you were referring to (page 128) :
"In truth, most Fender OTs will pretty easily tolerate an impedance mismatch of a factor of two in either direction (ie, halved or doubled)."

way cool jr · **Joined:** Tue May 18, 2010 7:34 pm **Posts:** 6911

DVM

i know what you mean about opinions.
if i didnt like the amp this thread would have never started bro. :wink:

i love it actually. i liked the tone so much that i bought the entire rig off the
guy that showed it to me. yep guitar,pedal,amp,strap everything.
had to have that tone exactly as i heard it with my own two ears so i bought
all of it. so yeah, i like the amp very much lol.

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