holiday model 204.

[DummyLoad]

picked this amp and monkey wards airline 62-9013a (similar to silvertone 1472) up today from a friend. couldn't find a schematic for it so it was first up on the bench to be reverse engineered. saw topic on another board where they discuss this amp. most state it doesn't have power transformer. it's not a death trap amp per-se, but the heater string is tied to the wall. meh! at least B+ is isolated and neutral is floating. will snip out the line filter cap and add a 3 wire power cord.

cool looking amp. speaker has big chunks of cone missing, so i'll need to round one up: it's an 8 inch - any recommendations that won't bust the wallet?

interesting topology - 12AU6 pentode >> TS >> 12AV6 CF >> level control >> 50C5 output - i guess they needed another tube to burn up the needed 12V on the heater string for the sum of 110V, but didn't want any additional gain - OK let's make the damn thing a CF then...

some pics of the chassis in the link below. pics of the amp will follow when and IF it's returned to service. transformer test good, but ya never know. doug you may want to add the schematic to the schematic library?

https://www.dropbox.com/sh/57r2z2js2oe48m0/AABSuV679L3roGl_msI6TcuDa?dl=0

--pete   

[TIMBO]

Cool stuff. 

[mresistor]

I have never tried one but saw these ..  https://www.sweetwater.com/store/detail/Eight15--celestion-eight-15-8-inch-15-watt-replacement-guitar-speaker-4-ohm they come 4,8,or 16 ohm.

is the ot output 4 or 8 ohm?  schematic says 8 ohm 

[DummyLoad]

thanks for the feedback, guys. 


--pete

[PRR]

> heater string is tied to the wall. meh! at least B+ is isolated and neutral is floating.

Transitional. It depends on heater-cathode insulation. In time even these got regulated away.

I don't like it. But knowing the motorcycle you ride, this is not the most dangerous toy in your life.

Your wiring shows V1 heater to "H" and rectifier to "N". Ideally should be other way around, preamp heater more groundy. IMHO an H/N reversal is more common than not, so it will be "wrong" 5%-60% of the time.

Yes, the AV6 is odd. It marginally raises gain (by unloading pentode). Odd that a 6AV6+parts was cheaper than a resistor.

The stock OT can't possibly be "5W" as noted. These were generally called "1W" and pretty crappy at half-Watt. Yours is bigger than most though.

[DummyLoad]

> heater string is tied to the wall. meh! at least B+ is isolated and neutral is floating.

Transitional. It depends on heater-cathode insulation. In time even these got regulated away.

I don't like it. But knowing the motorcycle you ride, this is not the most dangerous toy in your life.

Your wiring shows V1 heater to "H" and rectifier to "N". Ideally should be other way around, preamp heater more groundy. IMHO an H/N reversal is more common than not, so it will be "wrong" 5%-60% of the time.

Yes, the AV6 is odd. It marginally raises gain (by unloading pentode). Odd that a 6AV6+parts was cheaper than a resistor.

The stock OT can't possibly be "5W" as noted. These were generally called "1W" and pretty crappy at half-Watt. Yours is bigger than most though.

went by the cord polarity- ribbed is neutral, at least it used to be. agree preamp tubes SHOULD be closer to neutral. that's what i see, that's what i documented.    

agree about the heater string load resistor, not just the parts but the labor to wire it all up and chassis fabricator to punch the extra holes. had to be they were looking for pitch on tube count to sell, or possibly even tone mojo.

yes, brain fart on the OT watt rating - it's the same size as a fender reverb trans. so 2W at best. i'll fix the schema later. 

--pete

EDIT: fixed shema attached.

[DummyLoad]

mods i'm considering... want to use a triad n48x (size is perfect) but ALL the well known suppliers (mouser, allied, digikey, etc.) are out of stock. one guy on ebay wants 30bux a copy for what sells for 11 to 13bux elsewhere. another ebay seller wants 15 + 10 bux to ship.

i'll probably snip out the line filter cap - notes say Y2 class if i keep it.

V2 gets strapped as a gain stage - the layout is just begging for it. too much gain is not a sin - too much can be tamed. :)


original speaker measures 7.1Ω DCR. so likely an 8Ω. only cheap speaker i have is 4Ω. budget celestions are 16 or 4Ω. jensen or WGS seem to be the only economical choices. however, digging through my stache, i found 5 NOS JBL 8140 and they are 8Ω - don't know how it's going to sound as a guitar speaker, but we'll soon find out. 97dB efficiency. not bad. not bad at all. but the freq. resp. 30Hz-20KHz may be a problem.

http://www.jblpro.com/pub/obsolete/8140h.pdf

awaiting multi-section cap delivery & triad iso xfrmr. schema attached.

--pete

[PRR]

> JBL 8140 and they are 8Ω - don't know how it's going to sound as a guitar speaker, but we'll soon find out. 97dB efficiency. not bad. not bad at all. but the freq. resp. 30Hz-20KHz may be a problem.

That's a lie. 30Hz is 20dB down. Fs is 95Hz, Q is about unity.... this is a small guitar speaker (a better-class radio speaker).

I suspect more guitarish if you can snip out or at least disconnect the piezo(!!) tweeter without any other damage.

I would call that a 10 Watt guitar-rated speaker. In 1992 they could have been using a better grade of shellac and it might stand 20W of abuse (that's what they claim), but can't tell until it fails. IAC, more than the 204 can threaten.

[mresistor]

https://www.parts-express.com/celestion-eight-15-8-15w-guitar-speaker-8-ohm--294-2470?gclid=EAIaIQobChMIobrehMby3wIVkhh9Ch2AngnUEAMYAiAAEgJKzPD_BwE



https://www.amazon.com/CELESTION-Eight-15-ohm-15-Watt/dp/B00GMNG620

[DummyLoad]

https://www.parts-express.com/celestion-eight-15-8-15w-guitar-speaker-8-ohm--294-2470?gclid=EAIaIQobChMIobrehMby3wIVkhh9Ch2AngnUEAMYAiAAEgJKzPD_BwE



https://www.amazon.com/CELESTION-Eight-15-ohm-15-Watt/dp/B00GMNG620

cool! thanks for the link MRes!  of course i'm going to abuse the JBL though. y'all know that right? 

--pete

[John]

You???? Nahhhhhhh. 

[DummyLoad]

amp is a bust. nothing but an annoying buzz bomb. 1/2 wake recto for power - bleh! oh well 6 bux for parts plus time. gonna gut it some day and build P-P 6BQ5 10W with SSR FW PS. i'll keep the pentode front end. probably ream out the 12AV6 hole to take a 9pin for gain/cathodyne. on the back burner for now... IOW: it gets stuffed off into my storage room, until i stub a toe on it one too many times, when that point is reached, it gets sold off, scrapped or, morphed into some other abomination.

...where did i put those 6JB5?   


--pete