Originally posted by Rhodesplyr
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Magnatone Custom M10
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Originally posted by TelRay View PostSo, I am going for the 4FB2A1C
Actually no, I have a Horizontal Mount and the open side needs to be facing down. So, the last alphanumeric code needs to be a "B".
Need to respect the IMPEDANCE you guys have highlighted (1,475 - 2,250) and the INPUT and OUTPUT to be grounded.
So it'll be finally be a: 4FB3A1B (3 is for long decay)
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Originally posted by Diablo View PostYes, and Hammond has the patents on the spring reverb. They used to make them in house and then started up the Gibbs company to make them.
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Originally posted by Rhodesplyr View PostThe Ampeg Reverberocket is often cited as the first.
Didn't take long for Fender to dig their heels in, then dominate the market with their reverb amps. Meanwhile, score a point for Joisey!This isn't the future I signed up for.
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Originally posted by TelRay View PostDIODES:
For me it is clear that I'll go for the UF4007s to replace the IN697s (4 of them in the SCHEMATIC)
However I am not so sure (because of being different, probably for a good reason, form the other ones) about the 5th diode: CODI-575, the one connected to the 50V t/f secondary, 100 uF 50V cap and to pin 8 of the connector.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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Originally posted by Diablo View PostI have one of those necklace reverbs from a PR-40 tone cab. Is there any reason to use the necklace reverb over the conventional stretched spring tank for a guitar amp? Like I need another project.
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hello all, after some days out traveling for work I'm back working on the amp.
After re-constructing the POWER SUPPLY section (all resistors, capacitors and diodes - marked in green in the image below) and receiving the REVERB TANK I decided to plug it in for the first time.
As I have recently gotten a VARIABLE ISOLATION TRANSFORMER I started at around 40 VAC... no smoke, no jump in current... and gradually increased until 120 VAC. Plugged in the guitar with the amp cranked and got a glorious distorted sound, I really liked it.
The REVERB worked.
The VIBRATO is there, a bit subtle maybe.
The thing is, there's no clean sound, turning down the volume there is a crackling distorted guitar sound that fades away.
Checking the voltages, the main thing seems to be that I am not able to get the 400 VDC shown in POINT A (I'm at half of that, 211 V) and higher than I should on the BIAS VOLTAGE, pin 8 of the 12 pin connector (-67 V instead of -50 V).
My first doubt: is the Hammond 369BX the right transformer for this amp? (this is the transformer I got with the amp and there were all the evidences of the original transformer to have blown)
Here are the voltages measured at the Transformer Secondary (green and red actual values added to the table "ELECTRICAL DATA")
The voltages are OK, with the exception of the one going to the HEATERS and LAMP, which is 6.3 VAC instead of 7.01 VAC. But actually the amp's schematic shows a requirement for 6.3 VAC. So, I think this is OK too.
Until now, the TRANSFORMER does the job according to its specification (the TRANSFORMER's spec, not the AMP's spec)
Here are the DC values measured:
I honestly tried to figure out the way to calculate the DC Voltage provided by the Half Wave rectifier (the one with the single diode) and the one provided by the 2 pair of diodes in series but I got a bit confused.
Is it possible to extract some conclusions from these values?
- transformer to small for the job?
- something wrong with the way I re-constructed the POWER SUPPLY SECTION?
- etc
thanks!
PS: tested all tubes (with a Precision Apparatus tube tester) and all seemed to be in good shapeLast edited by TelRay; 02-03-2020, 04:34 PM.
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It's the transformer HV winding. Normally you would see something like 300-0-300 for that kind of rectifier arrangement (have a look at Fender Deluxe, etc.).Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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Originally posted by g1 View PostIt's the transformer HV winding. Normally you would see something like 300-0-300 for that kind of rectifier arrangement (have a look at Fender Deluxe, etc.).
mmm... i see. can I re-engineer the rectifier to make this transformer work or do i need to go shopping for a new one?
the same reasoning works for both the 400 V and -50 V shown in the schematic?
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You can use bridge rectifier with no center-tap for the HV. That will roughly double the voltage to where it should be.
But you will have to find a different method for the bias circuit as it will not work without the center-tap. Alternate methods would be a small separate transformer for bias, or the cap coupled type bias circuit.
Examples would be Ampeg V4 or Marshall JCM900 series, both using full-wave bridge and cap coupled type bias circuit.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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