| Author | Message | ||
     Arnie Lee |
Hi, Recently I replaced the phase inverter transistors in a friend's HD130 head. They had obviously been replaced at least once before. I used the NTE equivalent parts, NTE 196. I also tested each electrolytic cap on the driver board, and the diodes on the DB, and they are fine. I also replaced the original 100/450V filter caps. The 6CA7 Philips tubes in the amp are about 10 years old, and they test good for shorts, emissions and grid leakage on a small Sencore tube tester. Now, after about 5 weeks of using the amp on weekend gigs, the head is having problems again. The amp started to hum and had less power. The tubes got bright and the amp was shut off immediately to avoid red-hot plates. In checking it out last night, all voltages seem ok including the phase inverter board. It has no hum and output seems normal, but now I notice some distortion which remains there at different bias voltage levels. I realize this is probably a separate problem from the hum/output tube problem. I've checked the resistors and diodes that are soldered to the output tube sockets, but not the ceramic caps. There are four 1458G op amp IC's in this circuit. Any suggestions on how to proceed? I'm beginning to think one of the tubes could be going into an intermittent short somehow, under load. | ||
| Terry |
Hi Arine, I will try to help you out! First if you have 4/1458 /IC then you do not have a HD130 The HD130 used only one 1458 on the diver board. You have HD75 or HD150 Do you have reverb? How many tubes? If you do not have reverb then it is a base head. HD75 & HD150 all use 6l6GB tubes! No EL34!!!! The NIT196 /2N6292 is not what you should use, The right part #2N6488. This is the up dated part# and alot better. If we are going to help you, you must write back it will help every one!  | ||
| arnie |
Hi Terry, Thanks very much for the info on the updated 2N6488 part number, I will try a couple of those this week. Sorry for my confusing description of where the 1458 IC chips are located... there is only one of them on the driver board, and the other three 1458's are on the larger 'preamp' circuit board. It's a model HD 130 bass amp with no reverb, chassis #2100-130. Arnie | ||
| arnie |
...and the amp uses four EL34 output tubes. | ||
| Terry |
Arnie, I have not seen a HD130 with 1458IC on the preamp board. Just HD150! I would appreciate a little more info if you could ! I have repaired a lot of amps and not seen this. I do know, you never say it can not happen, because they were always changing what they were doing. If you can send me a PIC , that would be great. What is the # on the output Transformer 606-150 and what is the resistor 470/OHM on the power tubes. This is what my HD 150 has, and a BB3 circuit board. | ||
| arnie |
Terry, OK, now I understand... the 2100-130 schematic shows five LM307's on the preamp board. I don't have a camera or scanner for pics... but the preamp board is a BB2. The output transformer numbers are 4-130 over EIA606-001. The grid resistors on the power tube sockets are 220 ohm, 1/2 watt. Everything except the preamp section matches the 2100-130 schematic. The BB2 board looks like a factory installation, and not a hack-in. I'll do a search of the MM schematics to find the BB2 circuit. Thanks for your help. Arnie | ||
| Terry |
Arnie if you have the PVC 2000V/.001 no top of the power tubes take them out and put in ceramic dic 3000V/470 | ||
| nuke |
Check the 16V Zener diode, 1K 2 watt resistor and 20µf @ 25V capacitor on the driver board. This regulator circuit establishes a fixed 16 V bias point for the grids of the output tube. This frequently fails. I just fixed one recently with the intermittant problems as described in this thread. You can do a quick check on the circuit with the amp on standby and no tubes installed. Just measure the voltage on the zener side of the 1K 2 watt resistor and monitor it for a while. If you can use a *mild* heat gun to raise the temperature to operating level. FWIW, I usually uprate the wattage of the zener to a 5 watt type. Doesn't cost much and it's a more robust part. | ||
| Damien Trinkkeller |
why is there no diagrams for the bb2 board?! i have a seventy-five head sn#AN03000 with the bb2 & db2 boards and no schematics for the 75 watt! | ||
| Damien Trinkkeller |
ive tried the nte196, and the nte331, (2n6488) the nte331 sounds more bright and shimmery, way better high end, great for clean.. but very weak for distortion in my opinion, its double the duty of the 196, as far as voltage, current,gain.. etc........which i think the circuit cannot push the transistor hard enough to work correctly.....tell me what you think! | ||
| Steve Kennedy |
"why is there no diagrams for the bb2 board?! i have a seventy-five head sn#AN03000 with the bb2 & db2 boards and no schematics for the 75 watt!" The schematics are listed by chassis number. The seventy-five watt amps are found in "2100-75", "2275-75", and "2475-75" chassis. These schematics are available online. Some schem,atics have multiple versions in the file. Music Man was not very good about consistently referencing board layout numbers to schematics and what we have is courtesy of the current Music Man copyright holder (Ernie Ball, Inc.). What they have online is all there is to my knowledge. I just found out that the schematic link was broken... Ernie Ball changed their website (again) and broke my link. I will have to fix the link so we can have access again. | ||
| David Gereg (themilford) Username: themilford Registered: 10-2010 |
BUMP! I have a 65 with a BB2 board. It's a later transistorized bias (no 12AX7) model. I have not been able to find a schematic for this circuit. Mine has for DIP opamps as well (1458 I think). |