Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jukeboxman on January 04, 2018, 06:51:20 pm
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Hello i have 2 brasler 80 watt output push pull transformers
i was planning to use them in pushpull with 6l6 tubes the primary impedance is listed as 2200 ohms
i know the tube manual says 5k for 6l6 can i use these?
thank you so much gary
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Do you mean these? https://www.ebay.com/itm/Basler-Tube-Amp-Output-Transformer-2200-Ohms-CT-To-4-8-16-Ohm-80-Watt-BE32749001-/201585918254
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yes sir that is them
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Should work fine with a quad of 6L6s. Or, use with a pair of 6L6s by connecting an 8Ω speaker to the 4Ω tap, or a 16Ω speaker to the 8Ω tap, or a 32Ω speaker to the 16Ω tap.
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I'm a little but rusty on relected loads - but I'd say using 6L6 tubes in AB1 configuration you would have to double the impedance on each tap to keep the reflected impedance to the tubs at 4.4K.
Someone is going to come along and have a better answer I am sure .
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thank you guys ---i was thinking about reflected impedance but got all confused in my old brain
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I'm a little but rusty on relected loads - but I'd say using 6L6 tubes in AB1 configuration you would have to double the impedance on each tap to keep the reflected impedance to the tubs at 4.4K.
Someone is going to come along and have a better answer I am sure .
That's what sluckey said. Note: an OT does not actually have a primary impedance per se. It just has primary & secondary windings. The winding formula is complicated; but the reflected impedance it performs is simple arithmetic.
For this OT ea secondary tap reflects a primary impedance of 2200 ohms. For any tap on any OT, if you double the speaker load attached to it, then you double the primary impedance, as sluckey said.
Alternatively, a 50% mismatch either way is generally considered OK for guitar amps.
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Thank you all so much--i kind of knew that but my mind could not see it -the more i pondered it the more confused i got ----getting old sucks ---
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compare to other applications.
http://www.hammondmfg.com/guitarLineOT.htm (http://www.hammondmfg.com/guitarLineOT.htm)
as stated: 4 x 6L6GC is a good match for your OT. with sovtek 5881 you'll get about 80W with 450ish V B+.
--pete
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For example, if B+ is 450V at the plates and you want the tubes to run at 70% of their power, you can bias the 6l6's at 21 w. ( .70 times 30 ), which corresponds to aprox. .050A ( or50mA each tube, 200mA for a quad ).
Using señor Ohm's law, you get: 450= R multiplied by .2. We can find R (impedance or resistance) by dividing 450 by .2 whhich equals to 2250 OHMS primary impedance.
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then you give 50 OHMS to the waitress and with the other 2200 OHMS which corresponds exactly at your trannies, you're ready to go :laugh:
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Uncle Doug and El Paso have interseting videos I foind very informative. Here is Uncle Dougs
https://youtu.be/nNlPgirHP48 (https://youtu.be/nNlPgirHP48)
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Here's what Uncle Doug says that is pertinent to the discussion above .... and the OP should be apprised.
G5 posted this statement: I think most guitarists find a low-impedance mismatch preferable because a higher than nominal speaker can have especially bad consequences if a fly back voltage occurs.
And Uncle Doug responded : I agree that if impedance matching is not possible, it's preferable to have a lower speaker impedance (higher current) than one that is too high (higher voltage), for the reason you describe. Most OPT's can handle the increased current flow, but the output tubes can be damaged by the (sometimes much) higher voltage.
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So for my understanding in laymans turns. I have this OT on my bench now, Its Classictone’s 18 watt Marshall style with 10.8kohms primary for 4ohm speaker and 9.2kohm primary with 8ohm speaker. So If I used a 8ohm speaker on the 4ohm secondary wire Id then have a 5.4kish ohm primary? And if I used a 16ohm speaker on the 8ohm secondary Id then have a 4.1kohm primary :think1: that opens up more oprions for OT usage.
For a little more OT mid boggling El Paso just did another video on OT possiblities here
https://youtu.be/-xrXjw7nt-g (https://youtu.be/-xrXjw7nt-g)
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So for my understanding in laymans turns. I have this OT on my bench now, Its Classictone’s 18 watt Marshall style with 10.8kohms primary for 4ohm speaker and 9.2kohm primary with 8ohm speaker. So If I used a 8ohm speaker on the 4ohm secondary wire Id then have a 5.4kish ohm primary? And if I used a 16ohm speaker on the 8ohm secondary Id then have a 4.1kohm primary :think1: that opens up more oprions for OT usage.
Your understanding is backwards.
If you double the speaker load on the secondary, the load reflected to the primary will also double. I.E, for the transformer you mentioned, connecting an 8Ω speaker to your 4Ω secondary will reflect 21.6KΩ to the primary.
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Thanks Steve, by you telling me I have it backwards I went back to original post and got it. Thank you