Has anyone done the modification below?
Was any tweaking of the 6.8 Ω resistor required?
What are some of the tested transistor replacements for these Wurlitzer part numbers? 130537-5 130537-4 131262 131777
Would like to try on a 550 amp.
Thank you
Shankar Singh
Begin forwarded message:
From: Jay Hennigan via Jukebox-list jukebox-list@lists.netlojix.com Date: June 1, 2020 at 14:00:27 GMT-4 To: jukebox-list@lists.netlojix.com Subject: Re: [Jukebox-list] Bias adjustment W551 amp Reply-To: jukebox-list@lists.netlojix.com, Jay Hennigan jay@west.net
On 6/1/20 08:40, SFC(r) Rich Myers via Jukebox-list wrote:
Need to replace the output transistors on a W551 amp. Have sourced replacements NTE121(?).I think are the model. The current transistors are color coded green..not sure that is.as important today as it was back in the 60/70s.
As others have said, not adjustable. Check the values of the emitter resistors at 0.5 ohm (they're probably OK and difficult to check with most ohmmeters), also the voltage divider resistors on the base circuit.
Whenever I repair or rebuild amplifiers of this vintage with blown or previously replaced and mismatched germanium output transistors I will typically replace with silicon and change the values of the bias resistors to match. Looking through my notes I haven't done this swap on a Wurlitzer 551 so can't give you the specifics with 100% certainty but if you go that route, use MJ15016 transistors and replace the 2.7 ohm 2-watt resistors with 6.8 ohm in the base circuit. This should do the trick. Silicon transistors are more reliable and far less expensive than the generic NTE germanium parts available today.
-- Jay Hennigan - jay@west.net Network Engineering - CCIE #7880 503 897-8550 - WB6RDV _______________________________________________ Jukebox-list mailing list Jukebox-list@lists.netlojix.com http://lists.netlojix.com/mailman/listinfo/jukebox-list Searchable Archives: http://jukebox.markmail.org/