So I'm planning a 6V6 build for my parents for Christmas, but am having the most difficult time deciding on driverphase splitter. The amp will be used with a pair of small bookshelf speakers (NHT). The power transformer is from an old Motorola Console that ran PP EL84 (280-0-280) and a preamp section. The output transformers are Tamiko 5k 4/8/16 30w with UL taps. Amp must be autobias and have enough gain to be used as a integrated amp. They will more than likely use a cell phone (spotify) as the source. I was originally looking at the Dynaco/Acrosound schematic with 6SL7 as driver phase splitter, but not sure about the gain/drive capability. I would like to regulate the screens with VR tubes, but don't think I have enough voltage. Any suggestions?
If you have UL taps, use them and don't worry about regulating g2 B+. Frankly, I worry about a 5 Kohm end to end primary in combination with "12" W. multi-grid "finals" as being too low.
FWCT SS rectification of 280-0-280 and CLC filtering should give you plenty of B+. If a 5 VAC winding is available on the salvaged power trafo, 5AR4 vacuum rectification is a possibility.
The signal topology of "El Cheapo" should be just fine. The O/P of a "standard" 2 VRMS CDP is enough to drive the circuitry into clipping. Other than a somewhat fragile screen grid, the 'AQ5 shown is a 6V6 in a 7 pin mini package.
FWCT SS rectification of 280-0-280 and CLC filtering should give you plenty of B+. If a 5 VAC winding is available on the salvaged power trafo, 5AR4 vacuum rectification is a possibility.
The signal topology of "El Cheapo" should be just fine. The O/P of a "standard" 2 VRMS CDP is enough to drive the circuitry into clipping. Other than a somewhat fragile screen grid, the 'AQ5 shown is a 6V6 in a 7 pin mini package.
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You will have the option to drive the NFB loop from the 8 Ω tap.I have considered your design, but I have a couple of concerns;
I am not sure if this design will have enough drive for the bookshelf speakers as they are only around 86 db sensitive, but I have driven them with 2a3 amps with good results.
This amp will be going to my parents so as I really like the design and the CCS at the input, I would really like to avoid an amp that needs adjusting if a new set of tubes are installed.
I am not sure if this design will have enough drive for the bookshelf speakers as they are only around 86 db sensitive, but I have driven them with 2a3 amps with good results.
This amp will be going to my parents so as I really like the design and the CCS at the input, I would really like to avoid an amp that needs adjusting if a new set of tubes are installed.
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You can tweak the O/P tube operating point towards "aB", instead of the "Ab" as shown in the previously provided schematic. 15 WPC is about the limit for a PP 6V6 pair.
"El Cheapo" employs self biased O/P tube pairs. So, replacement is "PNP". Adjusting the CCS is a "1 time" assembly thing.
Paul Joppa's 102 dB. rule indicates that upwards of 32 WPC are appropriate for 86 dB. sensitive speakers. However, room size and listening habits have to be accounted for. If your folks like 19th Century "potboilers" from Berlioz, Liszt, Suppe ..., 6V6s and those speakers could easily be problematic. Small Jazz combos, chamber music, "easy listening", and many "pop" selections should be OK. If luck holds, even Haydn or Mozart symphonies will be pleasant.
"El Cheapo" employs self biased O/P tube pairs. So, replacement is "PNP". Adjusting the CCS is a "1 time" assembly thing.
Paul Joppa's 102 dB. rule indicates that upwards of 32 WPC are appropriate for 86 dB. sensitive speakers. However, room size and listening habits have to be accounted for. If your folks like 19th Century "potboilers" from Berlioz, Liszt, Suppe ..., 6V6s and those speakers could easily be problematic. Small Jazz combos, chamber music, "easy listening", and many "pop" selections should be OK. If luck holds, even Haydn or Mozart symphonies will be pleasant.
100 Kohm controls are unsuitable. 2X mono log. taper 10 Kohm controls are inexpensive. Look here. Also, check AA sponsor Jim McShane out. He offers parts for "El Cheapo" builders.
Cell phones and yours truly sort of get along. I have 1 of the non-"smart" phones for occasional use outside of my home. I'll take the word of "artsalo" regarding the signal level.
"El Cheapo" needs no additional gain, when the signal source is a "standard" 2 VRMS CDP. So, it seems an additional approx. 10X net voltage gain stage is needed. The better console power trafos will have both the heater and B+ current needed. A simple self biased common cathode 6CG7/6FQ7 section RC coupled to the LTP gets the job done.
"It's an ill wind that blows no good." The presence of an additional gain stage allows use of the already on hand 100 Kohm listening level control(s).
That's what I was afraid of. That's why I'm having a difficult time choosing a design.
I guess that could be true if you aren't a Christian....can I get an Amen?!?
Read post #11. The problem has been solved.
That's honestly what I was going to end up doing anyway, but was thinking 6N6P (I love that tube).
Sacred music is ancient. Freedom of conscience is a fundamental American value. Long ago, I served in the U.S. Army and was prepared to go to extreme lengths to protect that value. However, all of us need to remember that our rights end at the tip of the nose and the next person's rights start at their nose's tip.
Keep it civil is very good advice in all sorts of contexts.
Keep it civil is very good advice in all sorts of contexts.
The 6H6Π (6n6p) exhibits a high heater current draw of 900 mA. (1/2 again as much as a 6FQ7) and that might be problematic. The amplification factor (μ) looks good. The low RP of approx. 1820 Ω suggests unbypassed cathode bias resistors for local current NFB and high linearity will not be problematic.
Please locate and provide as much info. as can be gathered about the Motorola power trafo you propose to use.
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