Guild Thunderstar Bass - 3 questions

mellowgerman

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Hi everyone!
I just got myself a nice blue-face thunderstar bass head(as you can see in my avatar). Got three quick questions for ya:

1. Does anyone know the general time frame the blue-face ones were made? I've been trying to get an idea as to when it was built but there's no serial number search application and there's not a lot of info about these on the web...

2. I've heard that the "aux" out jack is for a second cabinet, so that when you hook one up in addition to the speaker out cabinet, they each run at half power. Is this true or just a rumor that could hurt my precious baby?

3. Does anyone know the minimum ohm load for these? I figured it was 8...

thanks for any input!
 

mellowgerman

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Hi everyone!
I just got myself a nice blue-face thunderstar bass head(as you can see in my avatar). Got three quick questions for ya:

1. Does anyone know the general time frame the blue-face ones were made? I've been trying to get an idea as to when it was built but there's no serial number search application and there's not a lot of info about these on the web...

2. I've heard that the "aux" out jack is for a second cabinet, so that when you hook one up in addition to the speaker out cabinet, they each run at half power. Is this true or just a rumor that could hurt my precious baby?

3. Does anyone know the minimum ohm load for these? I figured it was 8...

thanks for any input!
 

capnjuan

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Hi mellowgerman; your avatar isn't real clear but I think this is your amp:

tstarbass2tube.jpg


tstarbass01.jpg


Twin 6L6s out; 12AX7 preamp and 7247/12DW7 driver; 50 watts nominal power output. Our BBer matsickma might have a better idea of when these were in production but probably not sooner than 1965 and probably not later than 1969. Yes; you can connect another 8 ohm load at the Aux jack and not harm anything; that's why it's there and yes, the nominal load on the output transformer is 8 ohms. Hope this helps. CJ
 

capnjuan

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Hi mellowgerman; your avatar isn't real clear but I think this is your amp:

tstarbass2tube.jpg


tstarbass01.jpg


Twin 6L6s out; 12AX7 preamp and 7247/12DW7 driver; 50 watts nominal power output. Our BBer matsickma might have a better idea of when these were in production but probably not sooner than 1965 and probably not later than 1969. Yes; you can connect another 8 ohm load at the Aux jack and not harm anything; that's why it's there and yes, the nominal load on the output transformer is 8 ohms. Hope this helps. CJ
 

mellowgerman

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Thanks CJ!
that is sort of my amp. the thing is i have a blue-face one. i've heard they're built the exact same just from slightly different eras...
here's a better pic
DSC00648-1.jpg
 

mellowgerman

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Thanks CJ!
that is sort of my amp. the thing is i have a blue-face one. i've heard they're built the exact same just from slightly different eras...
here's a better pic
DSC00648-1.jpg
 

capnjuan

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Hi MG; yes - it's the same amp, just decorated a little differently. I'm only guessing but I think yours is a later model. Guild used red and blue on its faceplates to distinguish the Maverick Bass and Maverick Lead amps from the early 70s. Yours looks to be in pretty good condition. I looked all over for those small cabinet corners ... never did find them. Does yours look like this from the back (might not have the rectifier tube shown in the right/center of the pic)?

TCthunderbass01.jpg
 

capnjuan

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Hi MG; yes - it's the same amp, just decorated a little differently. I'm only guessing but I think yours is a later model. Guild used red and blue on its faceplates to distinguish the Maverick Bass and Maverick Lead amps from the early 70s. Yours looks to be in pretty good condition. I looked all over for those small cabinet corners ... never did find them. Does yours look like this from the back (might not have the rectifier tube shown in the right/center of the pic)?

TCthunderbass01.jpg
 

mellowgerman

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i have actually heard that the ones with a side handle are the earlier ones. any truth to that?
here's mine from the back. the power cable was replaced with a 3-prong grounded one.
also, mine doesn't have the rectifier. just the two power tubes. is the rectifier a mod?
DSC00655.jpg
 

mellowgerman

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i have actually heard that the ones with a side handle are the earlier ones. any truth to that?
here's mine from the back. the power cable was replaced with a 3-prong grounded one.
also, mine doesn't have the rectifier. just the two power tubes. is the rectifier a mod?
DSC00655.jpg
 

capnjuan

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Hi MG: don't know whether the handle location is a tell for production sequence or not. The amp in the rear-view pic belongs to an LTG BBer ThunderCat. No, the rectifier tube isn't a mod or anything. Nearly every Guild tube amp from that era had given up the tube rectifier in favor of diodes. A standby switch is a convenience on a tube amp but a necessity on an amp with a solid state rectifier. You still have a back panel; nearly every eBay Guild head is missing its panel. The test points on the far left are a good thing; allows you to use mis-matched tubes while maintaining the bias. Although this model was the 'value buy' in the product line, there are more expensive amps that don't have them. CJ
 

capnjuan

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Hi MG: don't know whether the handle location is a tell for production sequence or not. The amp in the rear-view pic belongs to an LTG BBer ThunderCat. No, the rectifier tube isn't a mod or anything. Nearly every Guild tube amp from that era had given up the tube rectifier in favor of diodes. A standby switch is a convenience on a tube amp but a necessity on an amp with a solid state rectifier. You still have a back panel; nearly every eBay Guild head is missing its panel. The test points on the far left are a good thing; allows you to use mis-matched tubes while maintaining the bias. Although this model was the 'value buy' in the product line, there are more expensive amps that don't have them. CJ
 

mellowgerman

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very cool!
so what is the difference between the two types of rectifiers and why do the solid states require the standby switch?
sorry bout all the questions i'm just so curious about this stuff and i wanna know so i don't do anything wrong in the future
 

mellowgerman

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very cool!
so what is the difference between the two types of rectifiers and why do the solid states require the standby switch?
sorry bout all the questions i'm just so curious about this stuff and i wanna know so i don't do anything wrong in the future
 

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silicon has less sag for quicker transients, but it hits the tubes with high voltage immediately. Tube rectifiers take a bit of time to come up to voltage and the tubes have time to warm up to operating temperature. Leave your amp set on standby for a minute when you turn it on and your tubes will last longer.
 

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silicon has less sag for quicker transients, but it hits the tubes with high voltage immediately. Tube rectifiers take a bit of time to come up to voltage and the tubes have time to warm up to operating temperature. Leave your amp set on standby for a minute when you turn it on and your tubes will last longer.
 

capnjuan

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Hi GM: all the tubes in a tube amp have cathodes that are directly or indirectly connected to ground. These cathodes are coated with metals which have the property that, when heated, quickly and freely give up electrons. The 'heaters' or filaments can be compared directly to a heating element on an electric stove. The stove elements use a lot more power but still have to warm up to be useful; same for tubes, the cathodes have to be warm to be useful.

In amps with tube rectifiers, there are at least three and sometimes four windings on the secondary side of the power transformer; high voltage AC that goes to the rectifier to be converted to high voltage DC, a 5VAC/ 2 to 3 amp winding that heats the cathode of the rectifier tube, a 6.3VAC winding that heats the cathodes in all the other tubes and, if the amp is 'fixed bias', there will be a set of taps for the bias voltage. Although the amp is turned on, until the tube rectifier begins to conduct - when it's heater (filament) is hot enough - there is no high voltage DC in the chassis. As the recitifier heater gets hotter, it converts / 'rectifies' the AC into DC for supply to the plates of all the other audio tubes.

In amps with solid state rectifiers, there are at least two and sometimes three windings; high voltage AC that goes to the solid state rectifier to be converted to high voltage DC, 6.3VAC for the heaters or filaments of the audio tubes, and a bias winding; most but not all solid state recitifier amps from the mid-60s on are fixed bias. When the power is switched on, the diodes produce high voltage DC instantly and that high voltage DC appears on the plates of all the audio tubes including the output tubes.

In a solid state amp, if the DC is present without time for the heaters to warm up the cathode, electrons are stripped off the cathode at a destructive rate until the heaters are hot enough to support the tube. Over time and without the filaments having a chance to warm up the cathode before DC appears on the plates, the cathodes will be prematurely stripped of their electrons, tone will suffer, and the tube will have a shortened useful life. Standby switches, besides allowing plugging and unplugging without turning the volume down, prevent the premature failure of the tubes. This is more important in older, two-channel combo amps that don't have channel-switching via a footswitch.

No right or wrong here other than making sure you turn the standby on (usually turns the heaters on) and then turn the power on and, in reverse, by turning the power off first and then the standby off. Standby switches are a requirement in tube amps with solid state / diode rectifiers and a convenience in tubes amps with tube rectifiers. CJ
 

capnjuan

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Hi GM: all the tubes in a tube amp have cathodes that are directly or indirectly connected to ground. These cathodes are coated with metals which have the property that, when heated, quickly and freely give up electrons. The 'heaters' or filaments can be compared directly to a heating element on an electric stove. The stove elements use a lot more power but still have to warm up to be useful; same for tubes, the cathodes have to be warm to be useful.

In amps with tube rectifiers, there are at least three and sometimes four windings on the secondary side of the power transformer; high voltage AC that goes to the rectifier to be converted to high voltage DC, a 5VAC/ 2 to 3 amp winding that heats the cathode of the rectifier tube, a 6.3VAC winding that heats the cathodes in all the other tubes and, if the amp is 'fixed bias', there will be a set of taps for the bias voltage. Although the amp is turned on, until the tube rectifier begins to conduct - when it's heater (filament) is hot enough - there is no high voltage DC in the chassis. As the recitifier heater gets hotter, it converts / 'rectifies' the AC into DC for supply to the plates of all the other audio tubes.

In amps with solid state rectifiers, there are at least two and sometimes three windings; high voltage AC that goes to the solid state rectifier to be converted to high voltage DC, 6.3VAC for the heaters or filaments of the audio tubes, and a bias winding; most but not all solid state recitifier amps from the mid-60s on are fixed bias. When the power is switched on, the diodes produce high voltage DC instantly and that high voltage DC appears on the plates of all the audio tubes including the output tubes.

In a solid state amp, if the DC is present without time for the heaters to warm up the cathode, electrons are stripped off the cathode at a destructive rate until the heaters are hot enough to support the tube. Over time and without the filaments having a chance to warm up the cathode before DC appears on the plates, the cathodes will be prematurely stripped of their electrons, tone will suffer, and the tube will have a shortened useful life. Standby switches, besides allowing plugging and unplugging without turning the volume down, prevent the premature failure of the tubes. This is more important in older, two-channel combo amps that don't have channel-switching via a footswitch.

No right or wrong here other than making sure you turn the standby on (usually turns the heaters on) and then turn the power on and, in reverse, by turning the power off first and then the standby off. Standby switches are a requirement in tube amps with solid state / diode rectifiers and a convenience in tubes amps with tube rectifiers. CJ
 
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