bias adjustement

I want to preface this with I'm a pretty big nob and have never touched a transistor or biased anything. I have however recapped my Harmon Kardon 930 to what seems great success. There are several guides on this site for biasing this receiver but non include pictures and thus I really can't...

Hi everyone! I have changed all of the capacitors in this power amplifier, including the filter capacitors, as the old Elna's were very swollen. In addition, I've replaced all relays as well. I am very happy with the results! Now, I need to adjust the bias in the "Normal mode" (class AB) and...

Hi Guys, I've bought a Recording The Masters SM900, and i've a Pioneer RT909. SM 900 https://static1.squarespace.com/static/62798251da32f57e31bea13d/t/62f2149f22e6b6134c31427e/1660032161030/fiche_sm900_rtm_2022.pdf https://www.recordingthemasters.com/audiotapes Could you please help me to...

Here are some tips which you might find useful when you have a bias problem. Below is a schematic snip of a driver board for an AU-517. TR06 (centre left) is the bias control transistor, just below it is VR03 the bias trimmer, the transistor and the trimmer are vital to the operation of the...

Hello Folks, I found a BA-2000 at a thrift store and was trying to restore it. I swapped all fuse resistors, relays, and caps. It took me a month to do all this. I was excited about finally using it with my JBL's but when I tried to adjust the bias, C37 on F-2661 blew open. My Mistake was...

I read a number of threads about bias issues with the P700 amp boards in the Marantz 2275 and in other Marantz units. A lot of great information freely shared by other members. I came away not completely clear on the best approach to restoring the P700 board and thought I would start another...

Hi all, after reading miles of posts I decided to ask you something: Last week I've bought from a friend a MC302 poweramp and a C220 pre (this is still under official warranty 'till 2023). He has not used them for months and decided to sell them. They are in really near mint condition, but...

I'm taking my 2255 amp & C29 pre-amp for service and cleaning to our local technician in our area as the potentiometers are scratchy and sometimes the left channel gets distorted intermittently. Our local technician has done LED upgrades, DC offset, bias adjustments, power meter...

I’ve been trying to adjust the bias on this receiver but when I clip the leads on R77+ And R79- I get no readings. It should be around 10mV dc when it’s adjusted correctly I’m getting absolutely no v reading. I’ve got good sound in both channels now after replacing some junk components but I...

I have a mint original R-1050 that I am tuning up and I want to set the bias. My PB-1062 board has no fuses? They were jumpered out at the factory it appears as the solder points are undisturbed. Do I just cut the jumpers?

Hi I have recapped my 1060 and powered up to set the bias but I am seeing C006 (Nichion 6800uF 63v) go to ~70v. Adjusting the R723 makes no difference. I have checked that the pots are all working. The other channel is at a reasonable level. Have any of you come across this before or able...

Hi AK I have an old AU-666 that has been recapped and gotten new transistors all around since it was in a really bad shape. However when i turn it on now it has a DC offset of around -28V on both channels measured with no load, and I have run my head into the wall as to why.. All new...

Hey everyone! Hope you're all enjoying the holidays! I once again found myself in a repair pickle and asking for the sage wisdom of members much more experienced than myself. Recently re-capped a Yamaha CR-1020 for a friend and first I ran into the issue with the misprinted polarity sign on...

aka NEC AUA-8000E aka MCS3865. Found two similar treads: https://audiokarma.org/forums/index.php?threads/help-with-idle-current-adjustment.578811/ https://audiokarma.org/forums/index.php?threads/idle-current-question-nec-aua-8000e-amplifier.893200/ but with no solution, couple of guys tried...

I have this great ST-70 that i bought from a fellow Ak'er. It is a very clean kit with the only "non standard" difference that the front sockets to check the bias have not been wired. I am debating if i have the skills to wire them myself (i might need step by step instructions like the ones you...

Hey everyone! Just finished recapping and cleaning up a Lafayette LR-1515 and it sounds great, but the heat sync gets really hot. Like too hot to touch. My guess is the idle current is way too high after re-capping the unit. Usually, this isn't a big deal for me if I have the service manual...

Hi guys, newbie to this forum. I’ve been using a Cayin A50T doe a good 7 years now. Recently been thinking of upgrading to Genelax GoldLion KT77. I was wondering what I should set my bias to once I’ve upgraded. The Cayin manual states 0.30 - 0.35vdc however I believe that is for EL34. can I...

Hello ! I noticed that my M4 Bias current needs to be re-calibrated somehow “often”. All electrolytic capacitors were replaced recently. Any idea ? Thanks

Hello, after finishing a long recap and resistor upgrade on my NAD 304, I was following the alignement procedure for offset and idling current. I did it one time and after listening some music for 10 minuts, I disconnected the speakers for a 2nd and final adjustment. While I was doing it the...

I picked up this ST-70 a few weeks ago and have been cleaning it, going over it and deciding on tube choice for when I set it up after Christmas. The wife's decorations require I take my system out for the holidays. I have a few questions. While going over the amp I noticed that whoever did the...

Hello all I just recapped my Sansui 5000X and at the end noticed a massive channel unbalance. The right channel is outputting about 10-20V (peak-to-trough: when the left channel was at -20 to 20, the right was at - 10 to 10 using a 1khz sine) less than the left channel. I hadn't noticed because...

Hey everyone! In desperate need of some help here. I'm working on an SX950 for a friend, and for the life of me, I can't seem to keep the output transistors on the right channel from frying. I've gone through this a few times now and it's getting very frustrating. I had everything working just...

Since there is no unique source of information on the bias for the Sony TA-8650, with no mention of changes from the 125mV in the original Sony Service manual in any service bulletin, and rumors from a Japanese forum of a required new value of 30/40mV, I decided to do a quick and by no means...

I've begun to notice a slightly louder than usual hum coming from my Mac MA230 that I use daily in my office setup. It has been about a year since I last reset the bias, so I decided to take it out of it's wood case today to make adjustments. After reviewing the manual, a voltage of 0.7v is...

Hey everyone, long time lurker, first time posting. A friend brought me a dead CA-800, would not power on and many signs of heat stress on main amp and power boards. Our thought was the PO has dumped a bottle of cologne on it due to it's aroma and the goop present everywhere inside. I've...