s-petersen
Scott
Amazing how many variations there are!
Magnavox Flea Power: Getting More Out Of The 8600 Series - A Lot More!
- Thread starter dcgillespie
- Start date
s-petersen
Scott
Almost exactly like mine, Check the voltage at the cathode resistors and compare to the "correct" voltage, if it is a little lower, then we have almost identical transformer voltages.
You are within 10% so it can be run this way without issues.
You are within 10% so it can be run this way without issues.
Morrism -- Your voltages are perfect. The schematic does say 120 vac, but that's more of a generic labeling primarily intending to show that the bucking connection now allows the unit to operate directly from a more modern "120 volt line", as opposed the stock design which requires external adjustment for long term dependability with today's typical line voltages. The actual DC voltages shown on the schematic are based on my developmental model when operating directly from my AC line, which typically runs like yours at 122.0 vac. The extra couple of volts over the schematic designated 120 vac is insignificant, but I applaud your effort to chase down any detail that seem out of line. It's the details that make all the difference!
Dave
Dave
Very Nice! I like the bias pots! Where did you come up with those in a 50 ohm rating?
I've lost a couple via 'non-return loans' as well. Got to be careful about that....lol
I've lost a couple via 'non-return loans' as well. Got to be careful about that....lol
indosmokejon
Active Member
I just finished building out 2 more of these units, which makes 4 total for me, one as a scratch build. I find the 50ohm 2-3 watt variety bias pots a little hard to come by and quite pricey. For the latest builds I just went with 100ohm pots, which obviously act as a 0-50ohm pot for the first half of their travel. 100ohm pots seem to be cheaper and more plentiful. Just something to consider.
I've run into this as well. Tried a number of different types of 50 ohm pots, everything from 'conventional' type media pots, to wire-wound versions, and even some small 'trimmer' pots. As stated by indo, the 50 ohm conventional pots are getting harder and harder to find and prices seem to be going up on them. So, I've 'stocked' a bunch of 100 ohm / 2 watt pots, and will probably be switching to those as I continue building this circuit. I too have dropped to the 100 ohm sensing resistor and now use 4.9V as the bias setting. I believe Dave 'updated' the bias section to include a 10 ohm resistor off the tube socket and 'to' the pot...giving that value more like 60 ohms when including the 50 ohm value of the pot. So, I'm pretty confident the 100 ohm pot is a good choice. I really liked the recessed adjuster......so I think I'll try a few of those next time. Tubetime, do you know the current capability of those pots..... 1/2 watt , 1 watt, more? Thx, TSD
indosmokejon
Active Member
Calling Dave Gillespie!!! I absolutely love your work. I have built 4 of these now. I have used your boards to rebuild a Dynaco sca-35 with fantastic results. I am watching for some Heathkit w-4’s in order to rebuild them for my father. I love your projects. My question is slightly off topic but I am curious if you have involved yourself in anything else Single Ended but higher wattage like you have this Magnavox? This amp you have created sounds so incredible, I want to make something as good but with 6 watts a side instead. I guess I caught the single ended bug! Is there a project out there that you have involved yourself in that fits this bill?
dallen9494
Member
Greetings! I just finished my third dgse-1, this time using Transcendar 7 watt OT's. Sounds incredible! I had to use a PT from a Maggie 8800 as the PT that was on my 8600 had the lower voltages. I had to add a 100 Ohm resistor to get the voltages correct. I'm going to have to try a scratch build on my next one, I think I reached the space limit on the 8600 chassis!
Regards,
Dennis
Regards,
Dennis
If I may,
I'm thinking 6wpc isn t going to significantly change what you're hearing.
I'm not sure what you want the extra power for but you're looking at less than a 3db jump.
I'm sure there will be fine suggestions for more powerful SE projects.
You might be better served by looking for more efficient speakers.
Good luck with your projects.
I'm thinking 6wpc isn t going to significantly change what you're hearing.
I'm not sure what you want the extra power for but you're looking at less than a 3db jump.
I'm sure there will be fine suggestions for more powerful SE projects.
You might be better served by looking for more efficient speakers.
Good luck with your projects.
At about 8 watts RMS of power output, a point of equilibrium is reached where above that point, it becomes more practical to produce power output with a Class AB1 push-pull design. No doubt if you want, you can get double that amount of SE power from a 6550 -- but its far more practical to get the same power from a push-pull 6BQ5 family of tubes design. Technical performance of the latter design will invariably be much better as well. Still, if SE sound is what you want, then practicality usually goes right out the window. As NJ says however, a doubling of power from about 4 watts a channel to 8 doesn't gain a whole lot of additional sound. However, with highly efficient speakers, it just might be the difference between bass that has reached it's limits, to ample bass -- particularly if a truly high quality OPT is used. Personally, on my "sometime" list is a SE 6L6GC project with capable OPTs, for 16 watts stereo capability. With my 101 db Cornwalls in my smallish (but I prefer to call it intimate) listening room, that will do justice to most listening sessions, other than when I want to dust the chandeliers!
Dave
Dave
indosmokejon
Active Member
I realize there is only so far you can go with single ended as far as wattage output. I also realize that this starts to get impractical in regards to transformer size right around 8-10 watts a side. I’ve never heard a single ended amp that runs on 6l6gc, kt88 or el34 though so I gues I am curious, just as much as wanting the extra power. I know that highly efficient speakers is what I really need, but at the moment that is not in the cards for me. I just sold my main pair that were 86dB and bought a new pair that are 92dB, so I’m inching my way there! Dave’s Maggie is 1.75w a side. My thought was that doubling the power to 3.5 and then again to 7 watts would get me an additional 6 dB, theoretically.
indosmokejon
Active Member
Thanks for the input though Dave, I appreciate it as always. You answered my question, and so for now, I will stop digging for a Gillespie project that doesn’t exist......yet!
I do plan to get to it, but do know that the modified Magnavox amplifier of this thread is good for 3.75 watts RMS per side, and on a good day will just nip 4.0 watts per side. A 6L6 project should be easily able to double that power level. Moving to more efficient speakers will make a night and day difference in your system -- much more so than doubling the power level.
Dave
Dave
indosmokejon
Active Member
Ok. Definitely. It’s sad that I have built 4 of these and didn’t know that the amp produces almost 4 watts a side. I thought it was doing 1.75 a side, about 3.5 total. No wonder nj Phoenix said I would only get about 3 more dB’s, he’s right. What an idiot i am. I will see myself out now!
