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JBL Studio L890 sounds nicer than Stadium

Accessing Cross Over Network in JBL Stadium/Studio

Using the Variac is not a good solution! Received the Variac this week, tried a lower AC mains supply of 110V to AA100 using the Variac, the amp appeared to be running cooler. It was found consuming only 99 Watts instead of the earlier 135 Watts. But when I measured the Voltage at the rectifier...

Dear Gordon, I would like to put the cover back. Why does 5R4GYB drop 50V? Does that mean it dissipates more heat compared to GZ34? What is your opinion about Heathkit AJ-12 AM/FM tuner? Thanks, Dominic

Power Consumption for AA100 was measured it is ~135 Watts @120V. Ordered a 500 Watts Philmore Variac from Fry's.com it will help me to lower the input voltage to 110V. Will wait for the Variac before using the AA100 regularly.

Replaced the 2 large capacitors last night- it took about 3 hours! Did not want to make a mistake with all the connections. It took more time due to the crowded connections and also because I replaced some of the old wires going from the capacitors to Ground and the PC board. (Reason for...

Dear Gordon, Thanks for the elaborate note. This is very helpful. Last night I installed the small perf board with the 4 trim pots. I have set the cathode currents to 28ma for each tube. Even after that left channel was still sounding weaker. Tried swapping 7199 - still same. Tried pair of...

Bias was imbalanced! - Left 21 mA & 36 mA Right 44mA & 31mA Thanks for your expert advice Gordon! Yesterday night I inserted the Cathod current sense resisters. I am seeing the following currents Left channel 21 mA & 36 mA Right channel 44mA & 31mA I also made a small perf board with...

Thanks for the quick reply Gary! So I will replace the old diode and Electrolytic Cap only when I change the grid bias arrangement tonight.

Thanks a lot Gary! I will change to these caps and also install the independent grid bias. The grid bias supply has only one diode (1/2 wave rectification). Should I replace that with a Bridge rectifier to reduce the ripple that is customary to 1/2 wave rectification?

Hi Gordon, I recently got an AA100, all original tubes - 2 of the 7591A redplated after about 10 minutes. After reading your excellent post, recapped 6 of the 0.1uF 400V coupling capacitors in the Power Amplifier PCB with Solen metallized polypropylene capacitors. After recapping 7591A...

Thanks cademan! I recapped 6 of the 0.1uF 400V coupling capacitors in the Power Amplifier PCB with Solen metallized polypropylene capacitors. After recapping 7591A tubes did not redplate. Grid Bias now reads -18.2 on all 4 tubes. The left channel now does not seem to have same power...

Last week I received a Heathkit/Daystorm AA100 that was in storage in an attic for more than 10 years. On inspection it was missing only the power switch knob. After a quick cleanup I connected speakers and turned it on - no action - turned out the power switch was bad, bypassed power switch...