bias adjustment

Dear all, I inherited a TA-4650 from my dad which had been idle for around 15 years. I used it with great enjoyment for more or less a year before noticing one of the channels was sounding more silent than the other. The difference wasn’t huge, but it was perceptible. Given the reputation of...

I have 2330B in for blown outputs. The customer was driving two 4Ω speakers and fried the driver board. I identified the many, many damaged parts.. Some transistors are unavailable so I used the recommended On-Semi replacements. I even managed source original output transistors. I could not get...

Hi has anyone serviced/ repaired a Setton AS 1100? I'm currently repairing and restoring this amp that has a few issues. The service manual suggests that the left bias current is set to 30 mA and the right to 70 mA Surely this can't be correct. Is this a misprint? Does anyone one what the...

After having had a bad experience with my R-1, blew the left channel, I just had to dig deeper into the problem. I found a difference between the schematic and the actual main board. The component in question is VR301 R and L. (Bias control) Here is the question: which of the two situation is...

Just picked up a recently serviced AIWA AD-F350. I was born and raised listening to my dad's AIWA F660 which was then sold by him after years of non-use in 2009. I remember well the mechanics and sound of these AIWA decks. I'm looking for the instructions/owner's manual, but in the meantime I...

So I've been working on a Sansui 7070 I just found in a barn. The relay didn't click when I got it so I replaced the fuse resistors on the driver board F2624. I then replaced four transistors that tested bad on the same board. I had no problems after this and it sounded pretty good. I set the DC...

This is my first post here so please forgive any transgressions. I must also express my gratitude to everyone who has posted before me, as I have found so much valuable information here already. I am restoring a pioneer SX-550. I have replaced the output transistors with TIP41/42 pairs, and...

Hello, Does anyone have/know the procedure for setting bias on the Reference 300R? I’ve looked through old posts and can’t seem to find what I’m looking for. Additionally, if you happen to have a copy of the schematic, could you share? Thank you, Ben

Greetings fellow audiophiles, Continuing with my partially restored HK 730 I decided to change the VR401 Variable Resistor (trimmer) since it was giving me issues and couldn´t get it past 13-18 mV. I used a Bochen 3296 W102 13 trimpot as a replacement...

A bias voltage design for TA-500, K-100, 500 Mono that's suitable for vintage & modern output tubes. There have been several discussions of the design of the Fisher “bias-voltage from heater-string” method that Fisher used to generate the negative potential needed to bias output tubes. Dave...

Greetings all, I'm rebuilding my 7055 but am in need of some HELP!! I am a novice/newbie to rebuilding vintage gear. That said, I have successfully rebuilt several Pioneers and Sansui's but this is my first go with a piece of SONY gear. I love the looks and particularily the sound from this...

Hi all, A few years back I bought a second hand Technics SU V8 amp which quickly became my favoured amp (slightly, over a Sansui AU-317 that I also like). Every so often I have set the DC balance, Clamp Voltage and ICQ without problem using a multimeter and the instructions in the service...

Back around 1995 I saw a "Free" post in HP's internal ads for a Scott LK-72. Luckily I was the first to claim it (a gold-face, neatly built unit, in mostly pristine condition). It came with original instruction book and a note saying one of the 0.1 uf was leaking and needed replacement. As...

In starting this thread, I would like to recognize that the amount of Soundcraftsmen information on this site is amazing. Goat67, Avionic, and Geode have provided massive amounts of information/guidance in dozens of threads that I have sincerely enjoyed. I have owned Soundcraftsmen products my...

Long story short: I received a pretty chopped Marantz 2285B for Christmas. It had been worked on before in a bad manner (blew traces, weird parts, different resistor values, etc). Had to redo a lot of stuff here and there but the main amp circuit board (P700) has become a nightmare now. It had...

Can't set Bias on a KA-7100 Having a problem with an ineffective bias trimmer on a Kenwood KA-7100. Got a KA-7100 to restore and after initial DBT test and a little de-oxit I tried setting the trimmers for center voltage and bias before the restoration. The Left channel trimmers would not...

Hello again. With the friendly help of expert members along the way, I'm just about done updating my Kenwood KA-7002 amp. I've replace all the electrolytics, all of the 2sc458 and 2sc871 transistors, the trimmers and a few other components. Also put new paste and insulators on the outputs...

I'm looking for a service manual and/or circuit description for the B&K ST-140 or ST-140M. I already have a few low resolution versions of the schematic, the minimalist owner's manual, and a one-pager on adjusting bias that applies to multiple amps. I'm not sure if they ever produced a model...

Dear Friends, I need help and advise on my BA 3000. I purchased this two years ago and fully recapped all the boards (with Elna Silmic ii) and reflowed the solder (audio note) on all the boards. Ran trouble free for six months then the transistors blew on the left channel. Replaced the Sanken...

Hello friends, greetings from Brazil. I'm doing the repair on a Marantz 2285b and I'm having a hard time getting the BIAS adjustment. DC OFFSET + - = 0vdc. Reading based on q710 ranges from 0.7vdc to 2.1vdc, stirring in the BIAS trimpot Base of q709 does not vary anything, staying at -0,800vdc...

I've just finished recapping a fine little Kenwood KA-4002 integrated amp and I'd like to adjust the bias. There are two trimpots on the main amp portion of the one an only board in this unit and the generic Kenwood bias adjustment guide link indeed listed the KA-4002 and a bias to shoot for...

Hey guys, I finally decided to attempt to repair the Pioneer Elite M72. The unit was stored away for many years because it was in protect mode (red) light. I have been doing some research because my limited experience repairing electronics, so I got into it and found the power Amp assembly...

edit post sorry double post

Greetings! I think I've read all the relevant posts and still have a question. I am working on a Spec 2 that someone else has worked on. I upgraded all the TO-220's, electrolytics, and bias relays on the amp channels. I had an open R61 (thermal sense supply) and protection lamp on the meter...

Hi all, one of the bias current trimming resistors (R767) on the power amp board has gone bad and I am looking for a suitable replacement. The service manual says it is 200Ohms but I'm at a bit of a loss as to what I'm looking for:idea: Any pointers would be most welcome! Cheers guys