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Discussion Starter · #1 ·
Wood Musical instrument Rectangle Electronic instrument Audio equipment

Local shop item in for a service which means cleaning all contact points(pots, jacks, switches, tube pins and sockets) and checking all solder points and wiring for breakdowns.

Client says it is a 65(I dont confirm yet) with "field resistors"(?) changed by an earlier tech to "increase the highs"(?). Pics and observations will be provided: it is always challenging to use/teach proper terminology when servicing an amp for someone who plays lots yet has no interest in workings other than results "by ear".

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Discussion Starter · #11 ·
The questionable 1500R grid leak is just fine at 1630R and all the blue moldeds also wonderful no leakage as usual for them....

Amp sounds great and the 5U4 concern, which is warranted(3 amp draw on the 5 volt supply instead of 2 amp of the suggested 5AR4), is changed to a 5AR4(GZ34) as shown on the diagram(s): the 25 volt drop/sag on the 5AR4 instead of the 50v of the 5U4 also livened the amp up a bit🙂

Plugging the amp into a new Celestion G12M cream 8 ohm and it became a much louder defined delivery system with more response from dial tone tweaks..big punchy bass, richer mids and clearer throughout the dials.

I lean toward agreement about the 5 watters installed...I will discuss with the owner(via joes music) and replace if requested...hopefully sell the guy a speaker too😊
 

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Discussion Starter · #14 ·
one of our members, silently by pm, reminds me that robinette and wayne of headstrong both feel the 1 watt 470R screen resistors were under rated by Leo(maybe ok when 115 was the wall voltage a different situation existed) and at todays 125 supply they should be at least 3 watt.
🤔
 

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Discussion Starter · #19 ·
I tried a bunch of speakers in my ‘64 Deluxe Reverb… I wanted more volume and a balanced punchy tone… the Deluxe has less gain than the Reverb model… so perhaps even better to bump it up. There’s a “chart” on the Gear Page where they poll folks with the question… “best speaker for a Deluxe Reverb?” The Eminence Alessandro won… I bought one from Q Components (a great shop that ships really fast!) and it was around $200. The GP doesn’t lie… superb in my ‘64!
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Yes that speaker which was stock in my Headstrong Corduroy was impressive; both nextgen and q are always super quick shipping with competative pricing.
 

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Discussion Starter · #22 ·
Client had requested 1 watt 470R screen resistors, .1 coupling cap in the first vibrato channel gain stage and two remaining power caps changed out...the coupling cap will probably reduce the noise on the vibrato channel volume pot and the remaining fresh caps may solidify the feel of the amp in general.
Will bag up the old parts to stay with the amp and use comp resistors, F&T lytics and sozo coupling cap
 

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Discussion Starter · #23 · (Edited)
Gas Auto part Cuisine Metal Font
Circuit component Fluid Passive circuit component Gas Rectangle

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After the f&t power cap install all the background noise when turning the volume pot is eliminated....one of the old EH 6v6 had overheated at some point to cook the blue printing to grey....new set tung sol matched set 6v6gt and biased with output transformer resistance method(maths involved ala mr. robinette)😉
Very happy amp now....picking up 1 watt 470r tomorrow morning and job done as requested
 

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Discussion Starter · #25 ·
Sorry to rain on your parade, but adjusting negative bias voltage is not proper way to adjust bias current.
New tubes are different than old stock and most likely that -35volts doesn't really follow requirement for bias current.
It might work but I would prefer to measure bias current.
Gotcha loud n clear. Thanks
 

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Discussion Starter · #27 ·
Years ago I built a plate current fixture to allow the monitoring of octal, pin 3 plates. I used an analog meter from a defunct VTVM and calibrated it for 100mA full scale deflection or FSD, through selection of the correct shunt resistor for 100mA FSD...custom made.
It has a switched, dual adapter interface that enables me to conveniently monitor a dual output configuration.
It is a low cost test fixture if you can scrounge up the parts.

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Very cool....i was reading about this type of contraption recently: the author had used two or three hand held meters in unison to achieve the result until he built similar...I used to have a simple store bought version called a BiasKing ? once..not sure where it went🤪
thanks Paul
 
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