Here's my Fi Primer Loftin-White, which I built a year and a half or so ago. However, after much tweaking of circuit voltages & modding components (mostly different cathode bypasses) to get the sound just right, it's practically a different amp. Tried several 5AR4's, but fred diodes are better sounding IMO, in this circuit. All transformers are custom Electra-Print, all tubes are Sovtek. This amp now really kicks out a clean, tight uncolored sound that seemingly defies its 3W rating.
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Keltern said:
Do they sound as nice and warm as they look?
Yes they do. Otherwise I wouldn't bother building them. No short-cuts..Tubes are expensive and I use well designed circuitry..
Bear in mind the LS is still the weakest link.
Again, an example of the top part of my garage forecourt. Bit over exposed but the electric blue is quite visible with 600V+.
richj
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T100 SE
This amplifier is meant to run with KR-Audio's T100 tubes but due to delay in the production of these tubes I am for the moment using 842VHD. The input stage is 12B4 and a triode strapped EL84 is driving an interstage transformer. The IS transformers (bifilar) are from Sowter, output transformers from Hashimoto. The power supply is separate and together with the 842VHD I am using a 500V PS. (For T100 I will increase the B+ to ~750V)
I have tested the bandwidth and transient response: BW: 10-75kHz (-3dB) and a quite nice square wave at 20kHz:
Under the conditions I am running the amp now, max Po is 7W, Zo=1.5R and the distortion is 1.2% 2HD, 0.15% 3HD, at 0.6dB below max Po.
Schematic for the T100:
Jan E Veiset
This amplifier is meant to run with KR-Audio's T100 tubes but due to delay in the production of these tubes I am for the moment using 842VHD. The input stage is 12B4 and a triode strapped EL84 is driving an interstage transformer. The IS transformers (bifilar) are from Sowter, output transformers from Hashimoto. The power supply is separate and together with the 842VHD I am using a 500V PS. (For T100 I will increase the B+ to ~750V)
An externally hosted image should be here but it was not working when we last tested it.
I have tested the bandwidth and transient response: BW: 10-75kHz (-3dB) and a quite nice square wave at 20kHz:
An externally hosted image should be here but it was not working when we last tested it.
Under the conditions I am running the amp now, max Po is 7W, Zo=1.5R and the distortion is 1.2% 2HD, 0.15% 3HD, at 0.6dB below max Po.
Schematic for the T100:
An externally hosted image should be here but it was not working when we last tested it.
Jan E Veiset
Really nice work Jane.
Here is a picture of my parallel single ended el34.
It is based on a design by Andrea Ciuffoli:
http://www.audiodesignguide.com/my/el34_pse/el34pse.html
Its got lots of power and sounds terrific. I worked a fair bit on the layout to eliminate any hum. It is dead silent when at max. volume. I also used larger value caps and hexfred rectification in the power supply...
It is grid biased and i am using cv4004 and cv4003 military triods, as well as two closely matched mullard XF-4 quads from 1977. Rectification is ss as I didn't have any more room in the chassis...
Here is a picture of my parallel single ended el34.
It is based on a design by Andrea Ciuffoli:
http://www.audiodesignguide.com/my/el34_pse/el34pse.html
Its got lots of power and sounds terrific. I worked a fair bit on the layout to eliminate any hum. It is dead silent when at max. volume. I also used larger value caps and hexfred rectification in the power supply...
It is grid biased and i am using cv4004 and cv4003 military triods, as well as two closely matched mullard XF-4 quads from 1977. Rectification is ss as I didn't have any more room in the chassis...
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Soulmerchant,
Asking, not criticising. Do you have any heat problems with the EL34s that close together? I am using 6L6GCs that way and found the temperature between them on the chassis up to 70 degrees - heats up the chassis considerably. I had to drill holes in the form of a cross and mount a small computer-type fan underneath each foursome.
Please advise of your experiences.
Thanks.
Asking, not criticising. Do you have any heat problems with the EL34s that close together? I am using 6L6GCs that way and found the temperature between them on the chassis up to 70 degrees - heats up the chassis considerably. I had to drill holes in the form of a cross and mount a small computer-type fan underneath each foursome.
Please advise of your experiences.
Thanks.