Hi - Apologies up front. I'll put the essentials first. Details further on 🙂 - This is the plan:
Audio source ==> Kenwood Model 500 Integrated Pre Out ==> Nakamichi EC-200 Active Crossover ==>
==> Kenwood Power In (< 200Hz)
==> Heathkit AA-151 Aux In to Power Amp Section (> 200Hz)
(Speakers: Bozaks and Altecs)
Questions:
1) On the Heathkit, is it ok to run a wire directly from the auxiliary input to pin 8 of the 6AN8? (Volume is controlled at preamp/crossover)
2) Can the 6EU7 and 6AU6 tubes be pulled? And/or other parts of circuits be disconnected?
3) There's a 33K resistor and 470K resistor/33uf capacitor in parallel on the Auxiliary input - Is this necessary?
4) Do I need to be concerned about component compatibility (voltages, impedances, etc?)
Additional mods considered for long-term project:
- lower wall voltage to 117vac via bucking transformer
- replace power cord and add IEC receptacle that includes fuse, capacitor & switch (taking front power knob and lamp bulb out of circuit)
- rework output tube bias for individual (or pair) adjustment
- rework power supply filters - lower capacitance / add choke
- add switch/circuit for UL/Triode (Class A) operation
Did I miss anything? ;-)
Thanks in advance.
Jeff
https://ia804702.us.archive.org/6/i...lifier Assembly and Operation manual_text.pdf
Audio source ==> Kenwood Model 500 Integrated Pre Out ==> Nakamichi EC-200 Active Crossover ==>
==> Kenwood Power In (< 200Hz)
==> Heathkit AA-151 Aux In to Power Amp Section (> 200Hz)
(Speakers: Bozaks and Altecs)
Questions:
1) On the Heathkit, is it ok to run a wire directly from the auxiliary input to pin 8 of the 6AN8? (Volume is controlled at preamp/crossover)
2) Can the 6EU7 and 6AU6 tubes be pulled? And/or other parts of circuits be disconnected?
3) There's a 33K resistor and 470K resistor/33uf capacitor in parallel on the Auxiliary input - Is this necessary?
4) Do I need to be concerned about component compatibility (voltages, impedances, etc?)
Additional mods considered for long-term project:
- lower wall voltage to 117vac via bucking transformer
- replace power cord and add IEC receptacle that includes fuse, capacitor & switch (taking front power knob and lamp bulb out of circuit)
- rework output tube bias for individual (or pair) adjustment
- rework power supply filters - lower capacitance / add choke
- add switch/circuit for UL/Triode (Class A) operation
Did I miss anything? ;-)
Thanks in advance.
Jeff
https://ia804702.us.archive.org/6/i...lifier Assembly and Operation manual_text.pdf
Thanks Dave!
I've been going through the online Heathkit assembly booklet and a hard copy of the Sam's Photofact schematic, comparing them against the actual amp wiring. The online forums have been a great help too, as have been YouTube channels, "Uncle Doug" and "BlueGlow Electronics". At this point, I think I have answers to my original questions.
One note: the Sam's schematic is different from theone in the Heath booklet as regards B+ voltages (e.g. Sam's lists 360V whereas Heath lists 390V.... and 375V in another spot in the schematic - Confusing. Based on a post on Audiokarma, I'm betting it's 375V. But, I'll know for sure when I measure.)
The plan is to remove all pre-amplifier circuitry. This will make it easier to understand and work on the Power Supply and Power Amp sections.
There will be two inputs:
1) to 10K volume pot then grid of 6AN8 (pin 8)
2) directly to 6AN8 (Power in) - I'm still trying to figure out placement of rca jacks close to pin 8
Caps and resistors for the power supply & power amp sections have been ordered. I may also order a choke. A happy suprise has been that many of the original components measured are still within spec (e.g. the 4 EL84 grid resistors are all within 1% of 470K). I've ordered a power cord, volume pot, input jacks and speaker binding posts.
Still looming in my mind though is the idea of taking the entire thing apart, cleaning it up really well, and rebuilding it to include at least some of the mods discussed on the forums (e.g. phono section re-work, line-level bypass, individual output tube bias, tone control discreet components, UL/Triode switch)
Cheers,
Jeff
I've been going through the online Heathkit assembly booklet and a hard copy of the Sam's Photofact schematic, comparing them against the actual amp wiring. The online forums have been a great help too, as have been YouTube channels, "Uncle Doug" and "BlueGlow Electronics". At this point, I think I have answers to my original questions.
One note: the Sam's schematic is different from theone in the Heath booklet as regards B+ voltages (e.g. Sam's lists 360V whereas Heath lists 390V.... and 375V in another spot in the schematic - Confusing. Based on a post on Audiokarma, I'm betting it's 375V. But, I'll know for sure when I measure.)
The plan is to remove all pre-amplifier circuitry. This will make it easier to understand and work on the Power Supply and Power Amp sections.
There will be two inputs:
1) to 10K volume pot then grid of 6AN8 (pin 8)
2) directly to 6AN8 (Power in) - I'm still trying to figure out placement of rca jacks close to pin 8
Caps and resistors for the power supply & power amp sections have been ordered. I may also order a choke. A happy suprise has been that many of the original components measured are still within spec (e.g. the 4 EL84 grid resistors are all within 1% of 470K). I've ordered a power cord, volume pot, input jacks and speaker binding posts.
Still looming in my mind though is the idea of taking the entire thing apart, cleaning it up really well, and rebuilding it to include at least some of the mods discussed on the forums (e.g. phono section re-work, line-level bypass, individual output tube bias, tone control discreet components, UL/Triode switch)
Cheers,
Jeff