I just found this chart
On the "Mullard 5-20 KT88 PP blocks" thread that perhaps explains things. These specs are for KT88 at 500VHT, cathode biased, so the exact values are obviously not relevant for my EL34 setup, but the take away is that the OPT primary impedance can vary by quite a lot, with only a marginal variation in power and distortion. It boggles my mind how forgiving tube circuits are! Thanks for the info Johan.
"Mullard 5-20 KT88 PP blocks!
On the "Mullard 5-20 KT88 PP blocks" thread that perhaps explains things. These specs are for KT88 at 500VHT, cathode biased, so the exact values are obviously not relevant for my EL34 setup, but the take away is that the OPT primary impedance can vary by quite a lot, with only a marginal variation in power and distortion. It boggles my mind how forgiving tube circuits are! Thanks for the info Johan.
"Mullard 5-20 KT88 PP blocks!
with only a marginal variation in power and distortion
Not really...
The OPT impedance is your load line that you trace.
It is not that important because you need to fix your goals first, like power. Do you intend to get 10, 20, 30, 50, 60 watts out of the EL34?
One thing is sure, fix bias is the best without any compromise if done properly.
Not really...
The OPT impedance is your load line that you trace.
It is not that important because you need to fix your goals first, like power. Do you intend to get 10, 20, 30, 50, 60 watts out of the EL34?
One thing is sure, fix bias is the best without any compromise if done properly.
Same as seen in the datasheet I cited.
Why should a tube have ANY preference?? (it has a range, not a "match")
You don't(?) look at a transistor and wonder "What impedance does this thing like?" (Again there is a range, no magic load)
These are all Valves, as our English friends say. I can use the same water valve to blast dirt off my truck or dribble mud out of my boiler. There is a maximum flow and maximum pressure, but I'd rarely push both ratings in the same job, and it can work for much smaller chores just fine.
Hammond has a file of winding data and puts it on iron. They are very good, for transformers. I would not look to Hammond for tube advice. If they choose to put a number on a thing, it may be what *their* customers (who may not be typical, or skilled in any art) say they want.
Just to put a little math on it. The -3dB frequency of an output transformer is related to the impedance of the plate circuit something like this:
f(3dB) = Z (anode circuit) / 2 pi L
with some little gremlins from primary and secondary leakage inductance, primary capacitance and primary to secondary capacitance to make it more complicated.
What about when you start from the other end of the equation... have transformers, want to make music with them. I’ve got a pair of OPTs that are a little off the beaten path, 30 watts at 10k a-a, no UL taps. Salvaged from an old amp with a burnt out PT, no tubes, and missing about half the wiring so no restoration. Seems like I could run EL34’s up between 450 and 500V, getting about half power compared to the normal data sheet application. Good idea, or should I be looking at a different tube type? Any other possible types I could use? I have a quad of 34’s in my stash, but they could find application in something bigger at some point.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.