Now that I finished the J5Mk1 everything works well. I followed close the wiring indications to reduce background noise and it is very low compared with other amps I heard. But switchg on/off Gain produces an audible pop-noise. Does anybody found a solution or at least a way to reduce such poping noises?
Best regards.
Alvaro
Re: J5Mk1: Higher volts at V2 only. Help!
Well, the problem was I missed to connect R11 to mass! Now all voltages are allright!
I completed J5Mk1, so I tested voltages before to connect the amp to a real speaker.
These are my voltages in J5 MK1 (expected values into brackets):
Without tubes, all tensions are OK everywhere, but V2 cathode is just 0.1V (0V).
Tubes installed, all tensions everywhere are OK, but V2.
I measured these values at V2:
- V2a anode: 247V (170V). Anode resistor R12 is 100K (100K).
- V2a cathode: 4,4V (1V). Cathode resistor R13 is 820R (820R).
- V2b cathode: 249V (173V). Cathode resistor R14 is 100K (100K)
Swapped tubes and nothing changed.
Tested circuitry schematics and everything seems OK. It seems like there is more current intensity at V2, hence higher voltages, but now I don´t know what to check. V1 and V3, heating wires and power suply voltages are all OK. What to check next?
Best regards.
Alvaro
[Blockierte Grafik: http://img265.imageshack.us/img265/2889/v2hc1.jpg]
Would be useful to use a Hammond125ESE OT, as replacement for standard 125E model in J5Mk1, for better bass response? While 125E lower bass roll off is 150Hz, 125ESE is 100Hz, so perhaps this change can worth. Wiring would be similar, choosing 5K as primary impedance, right?
Best regards
Alvaro
I am close to finish my J5Mk1. Its not difficult at all for a beginer like me;). If we compare it, or other MADAMP kits, with "boutique" amps, well, they look not too different at all!. Even some boutique amps look simpler that J5Mk1, but anyway they are 10x more expensive more or less. So I wonder why this price difference. It is just for being handmade?, more expensive components?, more research in design? Can this justify this high price. or is just marketing?
Best regards
Alvaro
Re: J5Mk1 16 Ohm: R19&R20 recommended values?
Hi Martin. Thanks for your reply.
I did not completed the J5Mk1 yet, but I am close to finish it. I go slowly in order to check twice and to avoid problems later. My purpose was to solder the right resistor values from the first time.
But if those resistors might be right even with OT output for 16 Ohm, perhaps I will not need to change them. All right. I will measure current at that point with a multimeter. If it is > 45mA I will have to increase these resistor values, right?
Best regards
Alvaro
I want to make J5MK1 for a 16 Ohm speaker directly (I do not have 8 Ohm speaker, but 16 Ohm).
From FAQ I know I have to change the values of R19/R20 in order to obtain a cathode current for < 45mA for V3.
My Hammond 125E OT has a primary impedance of 5600 with the secondary at 15 Ohm. While standard configuration for 8 Ohm is Pri. 4200 / sec. 8 Ohm. My problem is that I lack the knowledge required to calculate the values of R19/20 for 16 Ohm configuration.
So anyone can help me?
