Impedance matching

[xtian]

I built my Fiddy 50-watt 1987 amp <https://tubeamparchive.com/viewtopic.php?t=19042> using a Fender Bassman '59 reissue OT, which has only a 2-ohm output. My cabs are 4 ohms. It's been running OK with this mismatch, though the PT is heating up to around 115 F, and I haven't been playing hard yet.

Is it worthwhile looking into impedance matching? Can I add an artificial 4-ohm output, and would it be helpful?

What is inside the Weber Z-Matcher? Schematic? http://taweber.powweb.com/store/zmatch.htm

[alvarezh]

Hi xtian, I have one of those weber Z matchers, it should work, at least, it does for me.

As far as what's inside, if I recall correctly there are two transformers. The first one takes your output impedance from your amp you have selected and sets it up to match the input of the second transformer that in turn outputs your selected speaker impedance. This is just what I figure, I have not confirmed this, it's just seems logical to me but, I could be wrong.

All the best.

[sliberty]

Please explain the relationship between a mismatched OT and a hot PT - I am missing the connection here.

[tribi9]

Im playing a cab rated @ 8 ohms matched to an amp that wants to see 4 ohms. The PT does not get hot at all. I played last night for about an hour and a half straight and at the end of the session my PT was still cool to the touch.

[Kagliostro]

Weber WZC-50 - $30.00
Impedance Converter Transformer, 50 watts, 2, 2.6, 4, 5.3, 8, 16 IN and OUT

http://taweber.powweb.com/store/wzc50.jpg

Weber WZC-100 - $48.00
Impedance Converter Transformer, 100 watts, 2, 2.6, 4, 5.3, 8, 16 IN and OUT

http://taweber.powweb.com/store/wzc100.jpg

from this page

http://taweber.powweb.com/store/magnetic.htm



K

[rooster]

Yeah, I'm with sliberty here. In fact, the mismatch should cool things down as you are mismatched to the high side..

If your OT Is 115 degrees Fahrenheit then that's probably all filament/plate heat related, i.e., OT next to the over biased power tubes.

[xtian]

Please explain the relationship between a mismatched OT and a hot PT - I am missing the connection here.

I'm not suggesting there is a connection. Just opening a conversation. I guess I'll reevaluate after I have a chance to play loud for an hour.

[sliberty]

Please explain the relationship between a mismatched OT and a hot PT - I am missing the connection here.

I'm not suggesting there is a connection. Just opening a conversation. I guess I'll reevaluate after I have a chance to play loud for an hour.

Ok, I understand.

I am not really an expert, but my thinking is that if the OT mismatch were a problem, maybe the OT would be warm, but I don't really see how the PT would get warm unless the amp was pulling more current than the PT could handle. I doubt that the OT mismatch would cause that. Other things might cause a PT to heat up, like incorrect bias, or too small of a PT for the application. The OT mismatch is probably within a safe enough range to not cause any OT problems, but if I am wrong, I am sure others will provide more info.

[briane]

yep, PT being hot has absolutely NOTHING to do with the OT.

I think many misread your post and thought it was the OT heating up.

Likely too small PT for your power tubes - bad bias - or a shoddy PT.

oh, and a 50% impedenace mismatch is always within acceptable limits (not ideal, but no damage to be done either). Its only worth think about once your at the 200% (or 25% if smaller) mark.

[xtian]

Likely too small PT for your power tubes

Totally valid. I'm using a Bassman '59 reissue PT, which is meant to drive 6L6s. Though I'm not running a recto tube. No useful specs here: http://www.tubesandmore.com/products/P-TF36483

I had the power tubes biased for 70%. Maybe I'll go lower to ease the load on the PT.

[xtian]

With the Weber impedance matching transformer,

[img:501:545]http://taweber.powweb.com/store/wzc50.jpg[/img]

is the circuit really this simple? Just connect my amp's 2ohm output to the tranny, and choose an output tap from the tranny, like my attached napkin sketch?

[gldtp99]

Instead of buying an impedance matching transformer--- just buy the proper OT---- this Mag Comp OT is an excellent sounding unit and has 4/8/16 ohm output taps---i use a lot of these OT's.............................gldtp99

OT link: http://www.classictone.net/40-18001.html

[Roe]

+1 on classictone transformers

[xtian]

Well, fine, yeah. But the Classic Tone tranny is $70, and the matcher is only $30. Being cheap, here.

[xtian]

So is my implementation correct?