Hello,new to this forum. Is there anybody here on this site that can give me and idea of what output transformers to choose? I am a paint by numbers guy and do not have much exp in electronics. also any input on the design of this circuit and board ,,would be apreciated.
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The 1642SE is rather high impedance. I suggest the 1630SEA.
Cheaper Hammond 125ESE will also work. It's advertised for 100Hz but since you're output power will be <8 watts it will actually work down to lower frequency. Depends on your budget.
Other cheap Edcor options:
https://edcorusa.com/collections/tu...-5k-ohms-single-ended-tube-output-transformer
https://edcorusa.com/collections/tu...s-single-ended-guitar-tube-output-transformer
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I have been using the Hammond 125Ese on a build and they go much lower than 100hz. What is stated on the spec sheet is at full output power, not the way Edcor rates their transformers. Edcor does not state at what power the test their transformers at when you look at their frequency response. Advertising can be deceiving unless you can see a spec sheet. Look closely at the spec sheet graphs of the Hammonds and you will see how good the 125 series of OPT's really are. And that graph is at full output power. At a more normal power output for a hi-fi amp the frequency response is excellent. George Anderson confirmed this many years ago while designing and testing his projects. One can confirm this themselves testing their build using the Hammond 125 series of transformers. There is not a lot of difference in the price of a 125cse vs 125ese so go for the larger transformer is the way I see it.
You know, I thought I posted the 3k5 OPT, my bad!
Chinese alternative for a Chinese amp? https://www.aliexpress.com/item/100...00026205824599!sea&curPageLogUid=lpM7kVuFngGd
These are the figures George Anderson found with the Hammond 125Cse's.
Hammond 125CSE
These have been the best choice in low cost transformers. Best sound is achieved at 70mA. This transformer makes about 1 watt more above 100Hz than the Electra-Print. Specs at 1 watt: frequency response is 11.7Hz to 42.9KHz with 50mA, and 10.4Hz to 44.2KHz with 70 mA. Distortion is .65% with 70mA (mostly 2nd harmonic). Distortion is 2.6% at 6.0 watts. Low frequency effects at 5 watts: Visible saturation can be seen on the scope for any frequency below 77 Hz at 50 mA, 64Hz at 80mA. clipping was observed at any frequency below 130Hz with 80mA, but none was noted at 50 mA. Low frequency distortion tests at 1 watt: 100Hz lowest distortion was 1.01% with 63 Ma. At 36 HZ .66% occurs with 58mA.
ok, really appreciate all the info. I just purchased a pair of transformers from a boyuurange 50 for 120.00.....I guess i can also try the 125cse. I am just starting to get in to the tube stuff. Is there anything wrong with the circuit posted? Would i be better off with a point to point? is the B+ to low in this design.
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Also depends a lot on source and load impedance. Driven as "10k" with a pentode, I observed ~~150Hz. Driven low-Z (signal generator) it went toward 20Hz. A happy triode might give 50Hz-60Hz.
I agree. I would not use a board myself preferring point to point building such a simple circuit.
For what is worth, I got decent results using a cheap Chinese SE OPT. Details in https://www.diyaudio.com/community/threads/high-frequency-roll-off.385842/#post-7016572
That schematic does not match the photo of the assembled board. The schematic shows a pentode in the second tube position, strapped as a triode. The photo of the board looks like two 6SN7, two 300B, one rectifier. I suspect the topology it is 6SN7, 6SN7, 300B.
This board looks very similar to this board: 300B Board where the schematic showed two capacitively coupled stages but is in reality direct coupled and high distortion beyond low levels.
This board looks very similar to this board: 300B Board where the schematic showed two capacitively coupled stages but is in reality direct coupled and high distortion beyond low levels.
Hi to all, wanted to post my build on this eBay diy board. I am not an engineer or electric tech, just someone who decides to do random stuff sometimes . I basically build by the pictures. The power transformer has 320 0 320 and 3 sets of 5volts ..those are the yellow wires feeding the x2 300b and the rectifier tubes..the green wires are the 6.3v for the 6sn7 heaters..I believe those are parallel and i think the 2 300b heaters are dc ,,not sure?.....I did not try to modify anything because i do not know how so i just stuck to what ever came in the kit. When i turned the amplifier on for the first time i heard noise in on of the channels ..so i decided to swap my 6sn7 tube from left to right and the sound traveled with the tube...so i think one pre tube is bad.....my concern at this point is the hum from the transformer.I can put my ear to it and it seems to sing all by itself.....................please, I would appreciate any help with this also not sure if my connections in the amplifier are right
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That transformer looks like same one many vendors are selling on ebay:
https://www.ebay.com/itm/194930983639?
Not sure if you are in US? I'd suggest replacing the transformer first with this item. The vendor says will accept returns, if the problem is not solved.
If looking for different alternative-
I've had some good & some not so good results with Chinese sources. You can search my threads for problems I've had in the past.
Had good results with this vendor:
https://hifi-exquis.aliexpress.com/store/1100800846?
You can message them specs of your transformer, and see if they can provide better quality design.
Jim
https://www.ebay.com/itm/194930983639?
Not sure if you are in US? I'd suggest replacing the transformer first with this item. The vendor says will accept returns, if the problem is not solved.
If looking for different alternative-
I've had some good & some not so good results with Chinese sources. You can search my threads for problems I've had in the past.
Had good results with this vendor:
https://hifi-exquis.aliexpress.com/store/1100800846?
You can message them specs of your transformer, and see if they can provide better quality design.
Jim
Hifi-exquis definitely makes decent transformers, and customises many of them for free. I got a 40W push pull 10K from them, worked really well.
Their prices have gone up though, but still well below Hammond's.
Their prices have gone up though, but still well below Hammond's.
Hello to all. I would like to know if theres anybody on this site that could help me understand the operation of this Ebay tube amp i just built. I am sure that most people that build these amplifiers usually test before operation. I did the exact opposite simply be cause i do not have the tech knowledge, but this is the 5th amplifier ive built and guess what? all of them worked first start up and some are over 2years old and still working. I decided to build a 300b amp because i was told that the sound was different and what i have experienced so far is that this amplifier seems very smooth in the mid range and there seems to be quite a lot of it. First question?....would checking the bias voltage be a good first step? and what would the procedure be if so. I have posted the build pics. what other info would i need?